Russia-Aligned UAC-0099 Evolves MATCHBOIL Malware
ESET documents two years of UAC-0099 upgrades to its MATCHBOIL downloader used in espionage against Ukrainian government, energy and transport sectors.
ESET research published October 8 details how UAC-0099, assessed with medium confidence as Russia-aligned, steadily upgraded its MATCHBOIL C# downloader across versions observed from April 2024 to April 2026. Later samples adopted the Eziriz .NET Reactor obfuscator, sandbox-evasion checks, a two-minute C2 polling timer, and decoy GUIs such as a daily planner. Persistence shifted between Windows Registry Run keys and scheduled tasks. Victims include Ukrainian transportation, manufacturing and energy organizations, with activity observed as recently as June 2026.
- MATCHBOIL versions grew steadily more sophisticated between April 2024 and April 2026
- Late-2025 samples added Eziriz .NET Reactor obfuscation and sandbox checks
- Persistence shifted between Registry Run keys and scheduled tasks
- Victims spanned Ukrainian transportation, manufacturing and energy; activity seen June 2026
- ESET assesses UAC-0099 is Russia-aligned with medium confidence
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A Russia-aligned cyber espionage group has steadily upgraded its MATCHBOIL downloader over two years, adding stronger obfuscation, sandbox checks and changes to its execution and payload persistence.
In new research published on October 8, ESET documented MATCHBOIL versions compiled or observed between April 2024 and April 2026, finding that each version was more sophisticated than the one before it.
ESET attributed the malware to UAC-0099, a group that has targeted Ukrainian government organizations, financial institutions and media, and which ESET has assessed with medium confidence to be aligned with Russian interests.
The researchers said they had seen MATCHBOIL victims in Ukraine across transportation, manufacturing and energy, with activity observed as recently as June 2026.
MATCHBOIL was first documented by Ukraine's Computer Emergency Response Team (CERT-UA) in August 2025, but ESET found earlier samples suggesting development may have begun as early as April 2024. It is a C# downloader used to retrieve, install and establish persistence for additional payloads.
Obfuscation and Sandbox Checks
Earlier MATCHBOIL versions relied on unprintable Unicode characters and string encryption to make their code harder to inspect. By late 2025, UAC-0099 had switched to the Eziriz .NET Reactor obfuscator, which can use code virtualization and control-flow obfuscation.
The later samples also introduced checks designed to determine whether MATCHBOIL was running in a sandboxed environment. ESET said these capabilities were added gradually from late 2025, indicating a shift toward making analysis and automated inspection more difficult.
The downloader's execution model also changed. Earlier samples operated as one-shot downloaders, while a version from late 2025 ran on a two-minute timer, allowing it to retrieve a newer payload from its command-and-control (C2) server.
Persistence and Continued Development
The persistence mechanism MATCHBOIL set up for its payloads changed alongside its other components. The 2024 samples combined a Windows Registry Run key value with a scheduled task, while a July 2025 version relied on Run key entries. Later samples moved back to scheduled tasks.
Late-2025 samples also introduced a daily-planner-style graphical interface, displayed when MATCHBOIL was executed manually, although the researchers noted several inconsistencies that weakened the disguise.
A February 2026 sample instead displayed a less conspicuous utility for searching text files with regular expressions, suggesting the operators had moved beyond the planner.
The activity suggests UAC-0099 has treated MATCHBOIL as an evolving component of its toolkit rather than a static downloader.
"This demonstrates a keen interest by UAC-0099 operators in improving their downloader, not only to avoid detection by security solutions, but also to use it as a key part of their toolset in future attacks," ESET concluded.