Weaver Ant: A China-Linked Threat Group's Persistent Infiltration of Telecom Networks

Cybersecurity is a growing concern for telecom providers worldwide, especially when nation-state actors infiltrate their networks for extended periods. One such instance, detailed by Sygnia researchers, highlights the threat posed by Weaver Ant, a China-linked hacking group. For over four years, Weaver Ant exploited a telecom provider’s infrastructure, employing sophisticated methods to maintain stealthy access and conduct cyber espionage. This article delves into their tactics, techniques, and the broader implications for organizations facing similar risks.

Summary

Weaver Ant, a China-linked cyber espionage group, infiltrated a telecom provider’s network in Asia for more than four years. During a forensic investigation, researchers from Sygnia uncovered a range of malicious activities, including the reactivation of a compromised service account from an unknown server and the discovery of a China Chopper web shell.

The web shell, a tool frequently used by Chinese threat actors, provided the group with persistent access, allowing them to execute remote commands and move laterally within the network. Sygnia identified several web shells, including one novel variant called “INMemory,” which enabled attackers to execute payloads in memory, bypassing traditional detection methods.

The China Chopper variant used by the group employed AES encryption to avoid detection by Web Application Firewalls (WAFs), and it was deployed on externally-facing servers using ASPX and PHP. This allowed Weaver Ant to infiltrate the network without triggering automated defenses. Attackers used evasive techniques, such as inserting redacted keywords like “password” into the payload, making it harder to detect malicious activity through logs.

INMemory, in particular, was a highly advanced tool. It dynamically decoded and executed malicious code without leaving traces on disk, further evading detection. The attackers also employed recursive HTTP tunneling for lateral movement, utilizing compromised web servers as proxies to relay traffic and access internal resources.

Weaver Ant’s persistence in the network was reinforced by deploying multiple payloads, including those that modified Windows Event Tracing for Windows (ETW) and bypassed the Antimalware Scan Interface (AMSI). By manipulating PowerShell execution and leveraging SMB with NTLM hashes, the group expanded its access and continued its espionage activities.

The primary objective of Weaver Ant appeared to be network intelligence gathering, credential harvesting, and targeting high-privilege accounts within compromised environments. They focused on mapping out Active Directory networks to identify critical systems and users. Based on their tactics and tools, Sygnia concluded that Weaver Ant is likely a nation-state actor aligned with China’s cyber espionage goals.

What Undercode Says:

The Weaver Ant

From a technical perspective, the use of tools like the China Chopper web shell, combined with evasion techniques such as AES encryption and Base64 obfuscation, is indicative of a well-coordinated, highly skilled group. These methods ensure that their activity remains hidden, evading both automated defenses like WAFs and manual forensic analysis. The deployment of “INMemory” is particularly concerning, as it represents a shift toward even stealthier tactics, where malware resides entirely in memory, leaving no footprint on disk for traditional antivirus or endpoint detection systems to find.

The recursive HTTP tunnel is another innovative technique. By using compromised servers as proxies to relay traffic, the attackers avoid detection by blending their malicious traffic with legitimate web activity. This is a testament to the group’s understanding of network architecture and its ability to exploit common services for nefarious purposes. The long-term persistence demonstrated by Weaver Ant, combined with their ability to circumvent both automated and manual detection, underscores the importance of proactive threat hunting and continuous network monitoring.

Another striking aspect of this campaign is Weaver Ant’s focus on credential harvesting and Active Directory enumeration. By targeting high-privilege accounts, they gained deeper control over the compromised network, expanding their ability to exfiltrate valuable data. Their persistence and ability to operate undetected for years further support the idea that this is not just a criminal group, but a nation-state-backed operation with geopolitical motives.

This attack serves as a warning for all organizations, especially telecom providers and critical infrastructure entities. As state-sponsored actors continue to refine their tactics, it becomes crucial for companies to adopt more sophisticated defense mechanisms, including robust endpoint detection, threat intelligence sharing, and active defense strategies.

The geopolitical nature of this attack also reinforces the increasing role of cybersecurity in international relations. The attribution to China, based on factors such as the use of specific routers and operating hours, suggests that the motives behind such campaigns may be strategic, aiming to undermine the economic or political stability of rival nations.

Fact Checker Results

The use of China Chopper web shells is a well-documented tactic associated with Chinese cyber actors.
AES encryption and evasion techniques are common in advanced persistent threats (APTs) to avoid detection.
Weaver Ant’s activities align with known Chinese cyber espionage objectives, focusing on long-term, stealthy access.

References:

Reported By: https://securityaffairs.com/175800/apt/chinese-apt-weaver-ant-infiltrated-a-telco-for-over-four-years.html
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