CVE-2026-55206 Details
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.
A denial-of-service vulnerability has been identified in the py7zr library, which is used for handling 7zip archives in Python. The issue arises in the PackInfo._read() method, where an attacker can manipulate the numstreams value in the archive header. This exploitation leads to excessive CPU usage, as the method processes the data in a quadratic time complexity. The vulnerability affects py7zr versions through 1.1.2, with the problematic behavior occurring during the initial parsing of the archive, before any extraction takes place.
Users can upgrade to py7zr version 1.1.3 or later, where this vulnerability has been fixed. The update includes validation for the numstreams parameter to prevent excessive values, as well as an optimized calculation method that reduces the processing time complexity.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Jul 8, 2026CISA-ADP
Assessed Jul 9, 2026References to Advisories, Solutions, and Tools
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Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-407 | Inefficient Algorithmic Complexity | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| py7zr | <= 1.1.2 (semver) |
CPE
Remediation
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Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 9, 2026 | CVE Modified | CISA-ADP |
| Jul 8, 2026 | New CVE Received | [email protected] |