WinRAR Flaw Exploited by Russia-Aligned Groups to Deploy Stealers in Ukraine

Ravie LakshmananJun 09, 2026Vulnerability / Cyber Espionage

Two Russia-aligned cyber attack campaigns have continued to exploit a security flaw in WinRAR to target Ukrainian organisations, almost a year after patches for the vulnerability were released.

The activity has been attributed by Trend Micro to Earth Dahu (aka Gamaredon) and SHADOW-EARTH-066 (aka UAC-0226). It involves the exploitation of CVE-2025-8088, a path traversal flaw that allows an attacker to write files outside the extraction directory via NTFS Alternate Data Streams (ADS). It was patched by WinRAR in July 2025.

The findings show "how unmanaged software keeps an exploited entry point open long after the fix ships," Trend Micro researchers Hiroyuki Kakara and Feike Hacquebord said in an analysis published Monday.

The WinRAR exploit chain exploited by SHADOW-EARTH-066 is a departure from Excel macro droppers previously used by the threat actor to deliver an information stealer called GIFTEDCROOK. The latest iteration makes use of crafted RAR archives featuring a decoy PDF document and three hidden ADS payloads that are outside the extraction directory to initiate the infection.

This includes a Windows Shortcut (LNK) file that's placed in the Startup folder so that it's automatically executed every time a user logs in. This, in turn, spawns a PowerShell loader via "cmd.exe," which then uses in-memory DLL loading to ultimately launch an updated version of GIFTEDCROOK ("result.dll").

The malware targets passwords and cookies from Chromium-based browsers (Google Chrome, Microsoft Edge, and Opera) and Mozilla Firefox, in addition to harvesting documents matching certain extensions from the victim's machine. Once the data is exfiltrated to an external server, all malicious artifacts are deleted to cover up the forensic trail.

A notable change is the shift from Telegram as an exfiltration channel to dedicated command-and-control (C2) servers, a key modification that likely aligns with Russia's blocking of the messaging platform in the country earlier this February.

The second Russia-affiliated hacking group to weaponize CVE-2025-8088 is Earth Dahu, which has incorporated the flaw into its arsenal since at least September 2025. The adversary is known for its "industrial-scale effort" to maintain long-term access to compromised organizations.

"Earth Dahu used the vulnerability with an HTA-to-VBScript infection chain that delivered espionage modules," Trend Micro noted. "Based on RAR internal file timestamps and file naming conventions, the chain remained active through at least April 10, 2026."

These attacks, as recently also documented by Sekoia last week, lead to the deployment of GammaPhish, an HTML Application (HTA), which is then used to retrieve a VBScript downloader named GammaLoad. The intermediate downloader subsequently delivers additional modules like GammaSteel.

GammaLoad is "a collection of VBScripts designed to ensure continuous access and deploy payloads over time by leveraging Dead Drop Resolvers (DDR)," Sekoia said, adding it's used to deploy a dropper that's designed to launch a VBScript loader responsible for executing GammaSteel, a comprehensive information stealer that can monitor changes to files in real-time.

"WinRAR is deeply embedded in daily operations across Ukrainian organizations, making it an attractive target for exploitation," Trend Micro said. "The convergence of both established state-backed groups and independently tracked clusters on a single vulnerability reflects the scale of the cyber threats that Ukraine faces."

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