Medium6.5Red Hat Linux

Medium [CVE-2026-55206] Denial of Service via crafted.7z archives due to inefficient algorithmic complexity

This medium-severity Red Hat Linux advisory covers CVE-2026-55206.

CVE-2026-55206 Published Jul 8, 2026Updated by vendor Jul 8, 2026

CVE-2026-55206

Affected products & platforms

Red Hat LinuxUnclassified

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Summary

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 flaw was found in py7zr, a Python library for 7zip archives. A remote attacker could exploit this vulnerability by providing a specially crafted.7z archive.

This archive, when processed by the `SevenZipFile.init()` function, triggers an inefficient algorithmic complexity (CWE-407) during header parsing. This leads to excessive CPU consumption, resulting in a Denial of Service (DoS) for any application that opens untrusted.7z archives using py7zr.

This Moderate severity flaw in the `py7zr` library can lead to a Denial of Service. Applications that utilize `py7zr` to open or process untrusted `.7z` archives are vulnerable to excessive CPU consumption.

Red Hat severity: Moderate — CVSS 6.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H). Weakness: CWE-606.

Affected versions

< 1.1.3

Official advisory · high-confidence parse· fetched 10 days ago·verify at source

Fixed versions

1.1.3

Official advisory · high-confidence parse· fetched 10 days ago·verify at source

Mitigation checklist

Recommended fix / mitigation

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Official advisory · high-confidence parse· fetched 10 days ago·verify at source

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