What’s Vulnerable › Vulnerabilities

CVE-2026-55206: py7zr: O(n^2) algorithmic complexity DoS in PackInfo._read()

• Severity: high (CVSS 8.7 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-08 · updated 2026-10-25
• Weakness: CWE-407

Description

py7zr is a Python-based library and utility to support 7zip archive compression, decompression, encryption and decryption. Prior to 1.1.3, PackInfo._read() in archiveinfo.py used an O(n^2) cumulative sum pattern for attacker-controlled numstreams values parsed from archive headers, allowing a crafted .7z archive to cause excessive CPU consumption during SevenZipFile.init() before extraction. This issue is fixed in version 1.1.3.

Affected products

• miurahr py7zr: before 1.1.3

References

• https://github.com/miurahr/py7zr/commit/d7aa3a197d15c75a65b24f796d3a69f83806d3f8
• https://github.com/miurahr/py7zr/releases/tag/v1.1.3
• https://github.com/miurahr/py7zr/security/advisories/GHSA-h4gh-22qq-72r7
• https://github.com/miurahr/py7zr/security/advisories/GHSA-h4gh-22qq-72r7

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