CVE-2026-55781
NanaZip: Unbounded memory allocation (DoS) in NanaZip UFS parser via unvalidated fs_bsize/fs_fsize superblock fields
- Published
- Jul 10, 2026
- Updated
- Jul 10, 2026
- Assigning CNA
- GitHub_M
- Evidence observed
- Aug 29, 2026
Primary CVSS
nvd · CVSS 4.0
CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:XLow · next 30 days
- Percentile
- 4.6%
- Model date
- Oct 17, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
Summary
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.
Sources
Unbounded memory allocation in NanaZip's UFS handler via an attacker-controlled `fs_bsize` field.
PoCs & write-ups for CVEs I reported (coordinated disclosure; published + patched only)
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