Russian APT UAC-0099 Exploits AI Security Tools with GuardBreaker Prompt Injection
In September 2026, ESET researchers disclosed a new technique called GuardBreaker employed by Russia-aligned threat actor UAC-0099 against Ukrainian targets. The attack involved embedding provocative text about nuclear weapons creation into malicious VBS scripts to deliberately trigger AI safety mechanisms and prevent automated analysis. The technique aims to force large language models into refusal states, allowing malware like the MATCHBOIL loader to evade AI-assisted security workflows. This represents a sophisticated evolution in adversarial prompt injection, specifically designed to exploit the safety guardrails of modern AI security tools. This incident highlights the growing threat of AI-targeted evasion techniques as organizations increasingly rely on automated security analysis. With AI copilots and LLM-based scanners becoming standard in security operations, attackers are developing specific countermeasures to blind these systems, creating new vulnerabilities in modern defense strategies.
Kill Chain