Executive brief
7-Zip is a widely used file compression and archiving utility. A vulnerability in its 32-bit versions allows a specially crafted SquashFS archive to trick the software into reading and disclosing parts of the computer's memory during the extraction process. This could allow an attacker to steal sensitive information that happens to be stored in the system's memory at that time.
Technical details
An integer overflow vulnerability exists in the SquashFS ReadBlock function of 7-Zip 32-bit builds. The root cause is a lack of validation for the 'node.Offset' value read from the SquashFS inode. When calculating 'offsetInBlock + blockSize', a 32-bit unsigned integer wrap-around can occur, allowing the attacker-controlled offset to bypass fragment bounds checks. This results in a memcpy operation that reads heap memory preceding the cache buffer and writes it into the extracted output file. The issue is latent on 64-bit builds because the addition is promoted to 64 bits, preventing the overflow. The vulnerability was patched in version 26.01.
Affected products
- Igor Pavlov 7-Zip 9.34 through 26.00 (32-bit builds)
Timeline
- 2026-04-21: disclosed: Reported via SourceForge private issues
- 2026-04-27: patched: Version 26.01 released with fixes
- 2026-06-05: advisory: NVD publication date