CVE-2026-55781 NanaZip: Unbounded memory allocation (DoS) in NanaZip UFS parser via unvalidated fs_bsize/fs_fsize superblock fields
Attackers can cause memory exhaustion and application crash in NanaZip by crafting malicious UFS images with invalid superblock fields.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-55781?
CVE-2026-55781 is a low-severity denial of service vulnerability in M2Team NanaZip, published on 10 Jul 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
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.
Which versions are affected by CVE-2026-55781?
How do I fix CVE-2026-55781?
No fix has been published for CVE-2026-55781 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-55781 being exploited?
There is no known exploitation of CVE-2026-55781 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as GHSA-m34h-jf84-m74h.