Ransomware Raiders Riding the Windows Zero-Day Beast

Ransomware Raiders Riding the Windows Zero-Day Beast

In the wild, twisted carnival of cyber warfare, ransomware attackers have found a new toy to play with: Windows zero-day vulnerabilities. These are the digital world's equivalent of a skeleton key, undetected chinks in the armor, offering a straight shot past the guards at the gates.

By exploiting these hidden cracks in the fortress, these cyber outlaws can:

• Run malicious code like a bull in a china shop, wreaking havoc with full system access.
• Amplify the chaos of their ransomware onslaughts, turning Windows systems into their digital playgrounds.
• Boost the success rate of their attacks, ensuring that their ransomware hits its mark every time.

Peering into the heart of this madness, we find the Common Log File System (CLFS), a crucial cog in the Windows machine since 2003. It's used by both the OS and applications, relying on the clfs.sys driver. These logs are a mosaic of metadata in a Base Log File (.blf) and data containers whipped up by APIs.

The catch? Microsoft keeps the BLF format under wraps. But, like a map to a hidden treasure, it's decipherable through the art of reverse engineering, aided by debug symbols for clfs.sys.

Ransomware's new playground, exploiting Windows zero-day vulnerabilities, is something Microsoft doesn't scream from the rooftops. However, they do mention that CLFS is tweaked for performance, working with non-copy buffers that are flushed to disk.

Despite being a relic with an old code base, CLFS is riddled with vulnerabilities. We've seen over 30 elevations of privilege vulnerabilities patched since 2018, including four zero-days.

Diving deeper into the BLF file format, we unearth records stored in blocks, sector-sized reads/writes, and a CLFS_LOG_BLOCK_HEADER. The block header in BLF files contains sectors, checksums, and other less crucial info. The juicy bits for researchers are the RecordOffsets and the SignaturesOffset.

BLF files come in three flavors – CONTROL, GENERAL, and SCRATCH. The exploit finds its playground here, sidestepping the need for a prebuilt file. The records in these blocks, like CLFS_CONTROL_RECORD and CLFS_BASE_RECORD_HEADER, all start with a CLFS_METADATA_RECORD_HEADER, featuring a DumpCount field used by the ReadMetadataBlock function.

The GENERAL block is the treasure chest, storing key BLF data like clients, containers, and security descriptors. The CLFS_BASE_RECORD_HEADER structure, with its vast array of offsets, combined with symbols like CLFSHASHSYM and CONTEXT, creates a search-efficient environment.

The CLFS_CLIENT_CONTEXT and CLFS_CONTAINER_CONTEXT structures are where the real action happens. If attackers slip a malicious CLFS_CONTAINER_CONTEXT into a BLF file, unchecked, they can hijack the control flow and waltz right into elevated privileges.

In this madcap world of CLFS, performance is king, and sensible file formats are left in the dust. Disk offsets manipulated to cause structures to overlap create a playground ripe for exploitation.

To dodge these digital landmines, a new, more reasonable file format is the call of the hour. But until then, the Windows zero-day vulnerabilities remain a wild, untamed beast in the cyber jungle, with ransomware attackers riding it into the sunset.