Dissecting UAT-8099: New persistence mechanisms and regional focus

UAT-8099 is a malware campaign active from August 2025 to early 2026 targeting vulnerable IIS servers, primarily in Asia, with a focus on Thailand and Vietnam. It uses web shells, PowerShell scripts, and the GotoHTTP tool to maintain persistent remote access. New BadIIS malware variants show enhanced persistence, regional customization, and SEO fraud capabilities, with a Linux ELF variant indicating cross-platform targeting. The campaign shares infrastructure with the WEBJACK campaign, suggesting operational overlap. Although no known exploits are reported in the wild, advanced evasion and persistence techniques pose risks to confidentiality, integrity, and availability. European organizations with exposed IIS servers, especially those with business ties to Asia, should be vigilant. Targeted detection of web shells, PowerShell abuse, and monitoring for GotoHTTP traffic are critical mitigations. Germany, France, and the UK are most likely affected due to IIS usage and strategic interests in Asia.

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