Gamaredon's WinRAR Exploit: What Defenders Actually Need to Do
Russia's most active APT is weaponising a patched WinRAR flaw — here's the real-world detection and response playbook.
What Happened
Gamaredon (also tracked as Armageddon, UAC-0010) — Russia's FSB-linked APT that has been running non-stop offensive operations since 2013 — has added a WinRAR exploitation chain to its toolkit. The group is targeting Ukrainian government and defence organisations, but the TTPs are generic enough that any org using WinRAR is in scope.
The flaw being exploited is CVE-2023-38831, a path-traversal bug in WinRAR < 6.23 that lets a crafted archive execute arbitrary code when the victim opens it. It was patched in August 2023 — but patch adoption for a legacy utility like WinRAR is notoriously slow.
How the Chain Works
The delivery is a spear-phish with a .rar or .zip archive attached. Inside the archive:
- A decoy document (
.pdfor.docx) with a plausible filename - A folder with the same name as the document
- Inside the folder: a malicious script (
.cmdor.bat)
WinRAR's path-handling bug causes it to execute the script instead of opening the document. From there, Gamaredon drops GammaWorm — a .NET implant that beacons to Telegram-based C2 infrastructure and loads GammaSteel for credential harvesting.
Why Telegram C2 Matters
Using Telegram as a C2 channel is a deliberate evasion choice. Most corporate proxies and firewalls allow api.telegram.org outbound. You won't catch this with a blocklist unless you're specifically hunting Telegram API calls from non-browser processes.
Detection Opportunities
1. Patch gap detection (immediate)
Query your asset inventory for WinRAR < 6.23. Any host running it is a live exposure — prioritise patching before you build detections.
2. WinRAR spawning shells (high fidelity)
process.parent.name == "WinRAR.exe" AND
process.name in ("cmd.exe", "powershell.exe", "wscript.exe", "cscript.exe", "mshta.exe")
This fires on exploitation. Almost no legitimate WinRAR usage spawns a shell.
3. Telegram API calls from unexpected processes
dns.question.name == "api.telegram.org" AND
NOT process.name in ("Telegram.exe", "chrome.exe", "firefox.exe", "msedge.exe")
GammaWorm calls the Telegram Bot API from a .NET process. Flag anything that isn't a browser or the Telegram desktop app making this call.
4. Archive extraction into TEMP followed by script execution
Look for the pattern: file write to %TEMP%\*\*.cmd or *.bat within 5 seconds of WinRAR activity.
Response Playbook
If you get an alert from rule #2 or #3:
- Isolate the host — GammaWorm can move laterally before you react
- Pull Telegram API DNS logs for the host going back 7 days — establish the beaconing start time
- Check for credential access — GammaSteel targets LSASS and browser credential stores
- Review email gateway logs — find the delivery email, pull all recipients, check if it landed anywhere else
- Force password resets for any accounts authenticated on the host during the infection window
The Bigger Picture
Gamaredon's operational tempo is unusually high for a state-sponsored actor — they iterate tradecraft fast and accept detection in exchange for speed. If you're in a sector they care about (government, defence, energy, telco adjacent to Ukraine conflict), assume you're a target and treat this as a persistent threat, not a one-off campaign.
The WinRAR chain isn't novel — this CVE has been in attacker toolkits since late 2023. What's notable is that a well-resourced APT is still relying on it in mid-2026, which tells you the patch gap is real and wide.
TL;DR
- Patch WinRAR to 6.23+ across your fleet — this is your highest-ROI action
- Add the WinRAR shell-spawn detection rule to your SIEM today
- Monitor Telegram API DNS from non-browser processes
- If you're in a Ukraine-adjacent sector, treat this as a live threat, not a theoretical one