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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.

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.

Note: This information would facilitate lateral movement within the network and illustrates a clear intention to interact with other nearby hosts.

On completion of this scan, the .ndata.tmp file is moved to the filename .ndata.csv in the same directory. This file is exfiltrated immediately, and both files removed from the tmp directory.

The contents of this file will appear similar to:

INTERFACE = eth0 SOURCE = 192.168.0.2 IP begin = 192.168.0.0 IP end = 192.168.0.255 PORTS = PING off SCAN tcp *******start*scan********   Host 192.168.0.0: Host 192.168.0.1: tcp – 135:[ tcp – 139:[ tcp – 443:[ tcp – 445:[ Host 192.168.0.2: Host 192.168.0.3: Host 192.168.0.4:

The following command line parameters are present, but only a small portion is used:

-ip, -p, -o, -i, -noping, -udp, -n, -s, -t, -c, -h, –help

Command line help is also included:

Usage minmap -ip* -p* -udp -noping -o -t -c -s-i

td

The td utility provides Tor directory services and is compiled for ARM with no obvious modifications. The configuration for this is generated by the blob component, used for Tor management, described in the Components (blob) section, and saved at the path /data/local/prx.cfg. This file contains:

SocksPort 127.0.0.1:1129 PreferSOCKSNoAuth%sExitPolicy reject *:* DataDirectory /data/local/prx/ RunAsDaemon 1 HiddenServiceDir /data/local/prx/hs/ HiddenServicePort 34371 127.0.0.1:34371

This configuration provides a Socket Secure version 4 (SOCKS4) connection on the local port 1129 enabling the Tor network to be used. The blob component uses this for network connectivity checks.

The hidden service port is set to 34371 with the directory for hidden service information being set to /data/local/prx/hs/.

During the execution of td an .onion domain for a hidden service is randomly generated at the path /data/local/prx/hs/hostname which is then exfiltrated by netd. The db component performs further configuration detailed in the Multi-call binaries (Watchdog) section of this report to enable a SSH connection via this .onion domain. This gives the actor the ability to create an SSH session by connecting to the hidden service across Tor.

blob

The blob component is responsible for configuring Tor services and checking network connectivity. Every 15 seconds the tmp directory is checked for the blob utility, and if found, it is moved to the /data/local directory from the /data/local/tmp/blob directory, overwriting any existing version. Every 6,000 seconds (1 hour and 40 minutes) blob is then run from the /data/local directory.

netd executes blob which is responsible for configuring and executing Tor services provided by td. When run, it performs the following actions:

1. Checks local host for the port 1129 being open, exiting if it is.
2. Checks for the existence of /data/local/td. If this is not present, extracts it from /data/local/td.bz2 (bzip2 compressed data).
3. Creates the configuration file at the path: /data/local/prx.cfg. The contents of which are detailed in the Components (td) section above.
4. td is executed with this configuration file being supplied with the -f command line parameter: /data/local/td -f /data/local/prx.cfg.
5. db the modified Dropbear SSH utility is checked for at the path /data/local/db. If this file is not present, it is extracted from /data/local/db.bz2. db is then executed immediately after, with no command line parameters being passed.
6. blob then enters a loop where it performs a network connectivity check against the domain www.geodatatool[.]com connecting on the local SOCKS4 address provided by the td utility 127.0.0[.]1:1129 every 3 minutes.
7. It checks the second byte of the response from this domain to be the character Z (0x5a) to validate a legitimate response has been received from the server. Nothing further is done with the data; this is simply an internet connection check.
8. If this request fails or the server doesn’t return the expected data, blob terminates the execution of td.

tcpdump

The tcpdump utility (version 4.1.1) is compiled for ARM with no obvious modifications. This provides traffic capturing and monitoring functionality via the command line.

Multi-call binaries: db, NDBR_armv7l and NDBR_i686

The db utility contains multiple individual utilities which are selected based on the command line parameters supplied:

Utility	Actor	Modified	Description
dropbear	No	Yes	Dropbear SSH client with modified authentication functions as described in ‘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:

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

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.

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:

The following HTTP Post request is used to exfiltrate data:

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.