BianLian Hackers Exploiting TeamCity Servers to Deploy Powershell Backdoor

The infamous hacking community BianLian, known for its sophisticated cyber attacks, has shifted its heart of attention to extortion-most attention-grabbing operations following the liberate of a decryptor by Avast in January 2023.

GuidePoint’s Examine and Intelligence Team (GRIT) has been closely monitoring BianLian’s activities and, alongside with their Digital Forensics and Incident Response (DFIR) team, has uncovered a brand fresh capability of attack sharp the exploitation of TeamCity servers.

Initial Breach: TeamCity Vulnerabilities Exploited (CVE-2024-27198 and CVE-2023-42793)

The attackers exploited vulnerabilities identified as CVE-2024-27198 and CVE-2023-42793 to receive preliminary receive entry to, although the tell CVE passe remains undetermined due to unavailable logs.

This preliminary foothold allowed the menace actors to impress users and build malicious instructions beneath the TeamCity carrier chronicle.

TeamCity Server Exploitation

Upon gaining receive entry to, the attackers conducted reconnaissance the use of native Windows instructions and came all the scheme through extra infrastructure, alongside with two originate servers ripe for extra exploitation.

They deployed legit Winpty files to facilitate expose execution. They passe BITSAdmin to deploy a malicious PowerShell script, internet.ps1, and other communique tools with their expose and control (C2) server.

In a fresh breach, GuidePoint’s DFIR team detected malicious notify interior a shopper’s community that originated from a compromised TeamCity server.

After a lot of unsuccessful attempts with their normal GO backdoor, BianLian pivoted to a PowerShell implementation, providing the same performance. The PowerShell backdoor used to be obfuscated nonetheless not beyond deconstruction.

The GRIT team managed to decrypt and analyze the script, revealing its correct nature as a backdoor with capabilities corresponding to BianLian’s GO trojan.

Deeper Evaluation

The deobfuscated script published truffles and cookies functions, with the latter managing community connections and execution.

The script utilized Runspace Pools for efficient asynchronous code execution and established SSL streams for stable communique with the C2 server.

This diploma of sophistication permits for flexible and stealthy put up-exploitation activities.

Attribution to BianLian: Connecting the Dots

The GRIT team confirmed the backdoor’s affiliation with BianLian by inspecting tell parameters passed to the cookies draw and faulty-referencing IP addresses with known BianLian infrastructure.

Additionally, detections of the Microsoft AV signature Win64/BianDoor.D supplied extra evidence linking the PowerShell backdoor to BianLian.

BianLian’s skill to adapt and exploit rising vulnerabilities highlights the need for organizations to prioritize patching, incident response planning, and menace intelligence-informed penetration sorting out.

A proactive safety posture, combined with effective response capabilities, is vital to defending in opposition to BianLian’s and other cyber menace actors’ evolving ways.

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