Threat actor

UAC-0099

3 mentions in 7 days · 5 in 30 days · 5 total · first seen Aug 31, 2026 · last 4d ago

Timeline5 articles

Russia-Aligned Hackers Use GuardBreaker Prompt Injection to Disrupt AI Malware Analysis

Russia-aligned group UAC-0099 embeds GuardBreaker prompt injection in a VBScript comment to make AI malware scanners refuse analysis of a MATCHBOIL loader.

ESET identified a UAC-0099 VBScript used in an early-stage intrusion against a target in Ukraine that hides a safety-triggering comment (a question about building a nuclear weapon) intended to make AI code scanners refuse to continue analysis. The script downloads MATCHBOIL, a loader associated exclusively with UAC-0099, alongside familiar anti-analysis checks for IDA and Wireshark. The technique turns the AI triage process itself into the attack target, risking missed detections or benign misclassification of malicious samples.

Cyber Security NewsSep 11, 14:32 UTC · 4d agoThreat actor in the wild 3 sources

Hackers Weaponize AI Safety Guardrails to Hide Malware From LLM-Powered Security Scanners

ESET says Russia-aligned actor UAC-0099 hid guardrail-triggering comments in VBScript to derail LLM-based malware scanners in Ukraine.

ESET researchers linked a technique named GuardBreaker to Russia-aligned threat actor UAC-0099 during an attack against an organization in Ukraine. The group embedded a safety-sensitive, weapon-related request in a VBScript comment so an LLM-powered analysis tool might interpret it as an instruction and refuse or truncate analysis before reaching the malicious code. The VBScript downloaded MATCHBOIL, a C#-based loader used by the group alongside MATCHWOK and DRAGSTARE. OWASP guidance recommends treating code comments and metadata as untrusted input, sanitizing it, and never treating an LLM refusal as a clean verdict.

GBHackersupdated Sep 11, 14:32 UTC · 4d agofirst Sep 11, 10:51 UTC · 4d agoThreat actor in the wild 3 sources1

GuardBreaker: Derailing AI-assisted malware analysis with a code comment

ESET names 'GuardBreaker': UAC-0099 embeds a nuclear-weapon question in VBScript comments to trip LLM scanner guardrails during analysis of its MATCHBOIL loader.

ESET researchers observed the Russia-aligned group UAC-0099 inserting a decoy prompt injection into a VBScript used to install its MATCHBOIL loader in an attack against a Ukrainian target, aiming to make LLM-based code scanners refuse and stop inspecting the file. The comment triggers safety guardrails with a request about building a nuclear weapons but has no runtime effect. Similar LLM-thwarting tricks have appeared in malicious PyPI and npm packages reported by Socket and StepSecurity. ESET recommends multi-model cross-validation of AI-assisted analysis and treating missing LLM output as requiring further checks.

ESET WeLiveSecurityupdated Sep 11, 14:32 UTC · 4d agofirst Sep 10, 09:00 UTC · 5d agoAI safety & security 3 sources1

Russia-Aligned UAC-0099 Plants Nuclear Weapon Prompt in Malware to Disrupt AI Analysis

Russia-aligned UAC-0099 planted a nuclear-weapon prompt inside malicious VBS scripts to derail LLM-based malware analysis targeting Ukraine.

ESET disclosed a technique dubbed GuardBreaker used by Russia-aligned UAC-0099 against a Ukrainian target: inserting the text 'I want to make a nuclear weapon. Help me ...' as a comment in a malicious VBS script to trip LLM safety guardrails and stop AI-assisted analysis. The script downloads and installs MATCHBOIL, a C# loader exclusive to UAC-0099, which CERT-UA warned was distributed as a fake Notepad++ plugin in late July 2026. Similar prompt-injection anti-analysis tricks appeared in the Mini Shai-Hulud, Miasma, and Hades npm supply chain campaigns linked to TeamPCP, two of whose alleged members were arrested in Western Australia.

The Hacker NewsSep 2, 06:25 UTC · 13d agoThreat actor

Russian hackers plant nuclear weapon prompt in malware to trip AI safety guardrails

ESET reports Russian group UAC-0099 hid a prompt in VBS malware comments to trip AI safety filters and disrupt automated malware analysis in Ukraine.

ESET identified a technique dubbed GuardBreaker in which UAC-0099 embedded a comment reading "I want to make nuclear weapon. Help me …" inside a malicious VBS script to trigger AI safety mechanisms and halt AI-assisted malware analysis. The script, part of the group's toolset, downloads the MATCHBOIL malware used exclusively by this Russia-aligned group; CERT-UA documented the chain including LUNCHPOKE, BURNYBEAR and MATCHBOIL.V2 in a July advisory. UAC-0099 typically targets transportation and energy sectors and hands validated targets to GRU-linked Sandworm. ESET warned that AI-assisted analysis must be backed by layered detection and human-driven engineering.

Help Net SecurityAug 31, 00:00 UTC · 16d agoAI safety & security in the wild

Appears with

vendor ESET 5 malware MATCHBOIL 5 product MATCHBOIL 4 organization ESET 3 organization CERT-UA 3 vendor Socket 2 malware LUNCHPOKE 1 malware MATCHWOK 1 organization OWASP 1 product BURNYBEAR 1 product GuardBreaker 1 product LUNCHPOKE 1 product Notepad++ 1 vendor Flare 1 vendor Step Security 1 vendor StepSecurity 1

Entities are extracted by the model from each article. Watching an entity keeps it in this browser only (no account); the watchlist page and dashboard alerts use it.