Botnets Continue Exploiting CVE-2023-1389 for Wide-Scale Spread

Affected Platforms: TP-Link Archer AX21 (AX1800) Version 1.1.4 Build 20230219 or prior
Impacted Users: Any organization
Impact: Remote attackers gain control of the vulnerable systems
Severity Level: High

Last year, a command injection vulnerability, CVE-2023-1389, was disclosed and a fix developed for the web management interface of the TP-Link Archer AX21 (AX1800). FortiGuard Labs has developed an IPS signature to tackle this issue. Recently, we observed multiple attacks focusing on this year-old vulnerability, spotlighting botnets like Moobot, Miori, the Golang-based agent “AGoent,” and the Gafgyt Variant. Peaks caused by these threats are evident in the following figure. This article will explore their infection traffic patterns and offer insights into these botnets.

Infection - CVE-2023-1389

This is an unauthenticated command injection vulnerability in the “locale” API available via the web management interface. Users query the specified form “country” and conduct a “write” operation, which is handled by the “set_country” function. It calls the “merge_config_by_country” function and concatenates the argument of the specified form “country” into a command string, which is executed by the “popen” function. Since the “country” field won’t be emptied, the attacker can achieve command injection.

AGoent

AGoent is a Golang-based agent bot. It first fetches the script file ”exec.sh“ from ”hxxp://5[.]10[.]249[.]153,” which retrieves the ELF files of different Linux-based architectures.

After downloading the ELF files, the script will attempt to execute each file to find the appropriate architecture and remove each file to erase intrusion traces. The following analysis will focus on the executed file designed for the”386” architecture.

There are two primary behaviors. The first is to create the host username and password using random characters.

After user creation, the malware establishes a connection with the C&C (command and control) server and passes on the credentials just created by the malware.

Gafgyt Variant

Gafgyt, also known as BASHLITE, is malware that infects Linux architecture operating systems to launch a DDoS (distributed denial of service) attack. In this variant, the bot downloads the script file “bins.sh” from “hxxp://195[.]62[.]32[.]227” and then executes the script. Gafgyt retrieves Linux architecture execution files with the prefix filename “rebirth.”

We will next focus on “rebirth.x86.” Gafgyt gets the compromised target IP and architecture information, which it concatenates into a string that is part of its initial connection message.

After establishing a connection with its C&C server, the malware receives a continuous "PING" command from the server to ensure persistence on the compromised target.

The malware waits for any of the following commands from its C&C server. Each of them stands for a specified attack or function:

• ”UDP“ stands for ”UDP Flooding Attack”
• ”XMAS“ stands for ”XMAS Attack”
• ”VSE“ stands for ”VSE Attack”
• ”TCP” stands for ”TCP Flooding Attack”
• ”HEX” stands for ”defining specified string within attack packets”
• ”STOP” stands for ”stopping attack”

Moobot

Moobot fetches a script file from “hxxp://91[.]92[.]253[.]70.” The primary role of “1.sh” is to retrieve an ELF file with different architectures for further infection.

The following analysis looks at the execution file designed for the “x86_64” architecture. Once executed, it removes itself and erases all traces from the compromised device. It then displays “0x00000e9” in the console and starts contacting the C2 server “fjsnsinfinsf[.]ngcv[.]top”

Based on the XOR key “0xDEADBEEF” used for encoded strings and the hardcoded string “w5q6he3dbrsgmclkiu4to18npavj702f,” we can confirm this malware as Moobot. As the assembly indicates, a DDoS attack can be initiated on remote IPs via a C2 command.

Mirai Variant

Additionally, there is an attack using a variant of Mirai. The exploitation process begins by downloading “tenda.sh” from “hxxp://94[.]156[.]8[.]244.” This script file then downloads an ELF execution file from the same IP address, available in 13 different architectures.

The original execution file is compressed using UPX.

This Mirai variant displays the message, “faggot got malware'd,” and monitors processes to terminate those associated with packet analysis tools. It then sends packets to the C2 server “45[.]155[.]91[.]135:21425” and awaits additional instructions for attacking.

Below is an illustration of a DDoS attack scenario: The command and control (C2) server sends a packet with a length of 0x15, directing the endpoint to initiate an attack. The command specified is 0x01 for a Valve Source Engine (VSE) flood, with a duration of 60 seconds (0x3C), targeting a randomly selected victim's IP address and the port number 30129.

Miori

Miori, another Mirai variant, shares similar modules. The batch script is fetched from “hxxp://185[.]224[.]128[.]34.” The downloader employs both HTTP and TFTP protocols to retrieve the ELF files.

Once executed, Miori displays “your device just got infected to a bootnoot” in the console and sends \x00\x00 to the C2 server “rooty[.]cc” on TCP port 33335. The XOR key used for decoding configuration is 0xDFEDDEEF, and a hardcoded password list is included for the brute force attack function.

The attacking command packet resembles those seen in previous Mirai variants.

Condi

Condi’s downloader script was retrieved using multiple protocols to enhance the infection rate.

Condi is executed with the parameter “work,” which is included in the first packet sent to the C2 server “bn[.]networkbn[.]click.” The command remains consistent with the version distributed last year, retaining the function to prevent reboots by deleting binaries responsible for shutting down or rebooting the system.

It also scans active processes and cross-references with predefined strings to terminate processes with matching names.

Based on its selling page, Condi has updated its attacking methods, as shown below.

Conclusion

As usual, botnets relentlessly target IoT vulnerabilities, continuously attempting to exploit them. Despite the discovery and provided remediation for the vulnerability CVE-2023-1389 last year, numerous campaigns still exploit it, resulting in significant peaks in our IPS telemetry. Users should be vigilant against DDoS botnets and promptly apply patches to safeguard their network environments from infection, preventing them from becoming bots for malicious threat actors.

Fortinet Protections

The malware described in this report is detected and blocked by FortiGuard Antivirus as:

BASH/Mirai.AEH!tr.dldr
ELF/Mirai.A!tr
ELF/Mirai.BSC!tr
ELF/Mirai.CDB!tr
ELF/Mirai.GG!tr
ELF/Mirai.L!tr
ELF/Moobot.A!tr
Linux/Mirai.BSC!tr
Linux/Mirai.CEA!tr
Linux/Mirai.CJS!tr
Linux/Mirai.F!tr
Linux/Mirai.IZ1H9!tr
ELF/Mirai.AGIT!tr
ELF/Gafgyt.BJ!tr
ELF/Gafgyt.VE!tr
ELF/Gafgyt.WN!tr.bdr
Linux/Gafgyt.ARN!tr
Linux/Agent.AAO!tr

FortiGate, FortiMail, FortiClient, and FortiEDR support the FortiGuard AntiVirus service. The FortiGuard AntiVirus engine is part of each of these solutions. As a result, customers who have these products with up-to-date protections are protected.

The FortiGuard Web Filtering Service blocks the C2 servers and downloads URLs.

FortiGuard Labs provides IPS signatures against attacks exploiting the following vulnerability:

    CVE-2023-1389: TP-Link.Archer.AX21.Unauthenticated.Command.Injection

We also suggest that organizations go through Fortinet’s free cybersecurity training module: Fortinet Certified Fundamentals. This module is designed to help end users learn how to identify and protect themselves from phishing attacks.

FortiGuard IP Reputation and Anti-Botnet Security Service proactively block these attacks by aggregating malicious source IP data from the Fortinet distributed network of threat sensors, CERTs, MITRE, cooperative competitors, and other global sources that collaborate to provide up-to-date threat intelligence about hostile sources.

If you believe this or any other cybersecurity threat has impacted your organization, please contact our Global FortiGuard Incident Response Team.

IOCs

C2

fjsnsinfinsf[.]ngcv[.]top
45[.]155[.]91[.]135
rooty[.]cc
bn[.]networkbn[.]click
5[.]10[.]249[.]153
195[.]62[.]32[.]227

URLs

hxxp://91[.]92[.]253[.]70
hxxp://94[.]156[.]8[.]244
hxxp://103[.]188[.]244[.]189
hxxp://185[.]224[.]128[.]34
hxxp://5[.]10[.]249[.]153
hxxp://195[.]62[.]32[.]227

Files

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