CVE-2026-55206: CWE-407: Inefficient Algorithmic Complexity in miurahr py7zr
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.
AI Analysis
Technical Summary
The vulnerability in py7zr arises from an O(n^2) cumulative sum pattern in the PackInfo._read() method within archiveinfo.py. When parsing the numstreams value from a 7zip archive header, an attacker can craft a .7z file that triggers excessive CPU usage during the SevenZipFile.init() process before extraction. This inefficient algorithmic complexity can degrade performance or cause denial of service. The problem is resolved in py7zr version 1.1.3.
Potential Impact
An attacker can supply a specially crafted 7zip archive that causes the py7zr library to consume excessive CPU resources during archive initialization. This can lead to denial of service conditions in applications using vulnerable versions of py7zr, impacting availability. There is no indication of privilege escalation, data disclosure, or code execution from the provided data.
Mitigation Recommendations
Upgrade py7zr to version 1.1.3 or later, where the inefficient algorithmic complexity issue in PackInfo._read() is fixed. No other mitigation or temporary workaround is indicated. Patch status is not explicitly stated as 'official-fix' or 'patchAvailable' but the description confirms the issue is fixed in 1.1.3.
CVE-2026-55206: CWE-407: Inefficient Algorithmic Complexity in miurahr py7zr
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.
CVSS v4.0
Score 8.7high
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in py7zr arises from an O(n^2) cumulative sum pattern in the PackInfo._read() method within archiveinfo.py. When parsing the numstreams value from a 7zip archive header, an attacker can craft a .7z file that triggers excessive CPU usage during the SevenZipFile.init() process before extraction. This inefficient algorithmic complexity can degrade performance or cause denial of service. The problem is resolved in py7zr version 1.1.3.
Potential Impact
An attacker can supply a specially crafted 7zip archive that causes the py7zr library to consume excessive CPU resources during archive initialization. This can lead to denial of service conditions in applications using vulnerable versions of py7zr, impacting availability. There is no indication of privilege escalation, data disclosure, or code execution from the provided data.
Mitigation Recommendations
Upgrade py7zr to version 1.1.3 or later, where the inefficient algorithmic complexity issue in PackInfo._read() is fixed. No other mitigation or temporary workaround is indicated. Patch status is not explicitly stated as 'official-fix' or 'patchAvailable' but the description confirms the issue is fixed in 1.1.3.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-16T16:16:32.627Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a4eb690c9d9e3dbe3b68734
Added to database: 07/08/2026, 20:44:00 UTC
Last enriched: 07/16/2026, 10:05:00 UTC
Last updated: 08/22/2026, 22:52:14 UTC
Views: 74
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