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.
Other vulnerabilities in NanaZip
See all- CVE-2026-54616High
NanaZip from version 1.0.88.0 until stable 6.0.1698.0 and preview 6.5.1742.0 has a vulnerability in the Lz4Decode function that rejects only a zero return from LZ4_decompress_safe, while malformed input produces a negative error value. The negative int is converted to unsigned SizeT, leading to out-of-bounds read and potential data leak or crash.
- CVE-2026-55783Low
A vulnerability in NanaZip (a 7-Zip fork for Windows) prior to version 6.5.1749.0 causes a process crash when testing or extracting WebAssembly, ElectronAsar, Zealfs, Romfs, Ufs, Littlefs, and DotNetSingleFile archives. The issue stems from unconditionally dereferencing the caller-supplied Indices pointer, which can be NULL when the archive engine signals extraction of all items.
- CVE-2026-55782Low
NanaZip prior to version 6.5.1749.0 has a vulnerability in its WebAssembly archive handler where an attacker can control buffer allocation sizes. By crafting a file with manipulated NameSize and Information.Size fields, multi-gigabyte memory allocations can be forced, leading to memory exhaustion or process termination.
- CVE-2026-55780Low
A vulnerability in NanaZip (a 7-Zip fork for Windows) prior to version 6.5.1749.0 allows process crashes via a crafted .NET single-file bundle. The issue stems from missing validation of the extraction buffer size against the actual file size, potentially leading to std::bad_alloc or std::length_error exceptions.
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS