CVE-2026-55781
LowCVSS 2.4Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
A vulnerability in NanaZip (a 7-Zip fork for Windows) prior to version 6.5.1749.0 allows an attacker to cause memory exhaustion via a crafted UFS/FFS image. Missing validation of the fragment size (fs_fsize) lets a tiny image force multi-gigabyte allocations during open or extraction.
Risk Assessment
The organization is exposed to a denial-of-service (DoS) attack – opening a malicious file can exhaust RAM and crash the NanaZip process, disrupting user operations.
Recommendation
Upgrade NanaZip to version 6.5.1749.0 or later immediately. Until then, block unknown UFS/FFS images at the email gateway and in antivirus scanners.
Original NVD description (English source)
NanaZip is the 7-Zip derivative intended for the modern Windows experience. Prior to 6.5.1749.0, NanaZip's UFS and FFS image handler in NanaZip.Codecs.Archive.Ufs.cpp validates the superblock block size only against the MINBSIZE lower bound and does not validate the fs_fsize fragment size, allowing attacker-controlled 32-bit fields to flow into indirect-block, directory, and extraction buffer allocations. A tiny crafted UFS image can force multi-gigabyte allocations during open or extraction, causing memory exhaustion or process termination. This issue is fixed in version 6.5.1749.0.