CVE-2026-55206
High
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.
SeverityHigh
CVSS8.7
Exploit probability—
ProductPy7zr
PublishedJul 8, 2026
First seenJul 8, 2026
Weakness typeCWE-407CWE-407
How to fix
Update
- py7zr1.1.3 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| py7zrPyPI | v < 1.1.3 | 1.1.3 |
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