CVE-2026-55206CWE-407

py7zr: O(n^2) algorithmic complexity DoS in PackInfo._read()

High · published July 8, 2026

CVSS v4.0
8.7
EPSS
0%
Percentile
23.9
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
8.7 · HIGH
Vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
EPSS
0.00321 · 23.9th percentile
Weakness
CWE-407 · Inefficient Algorithmic Complexity
Published
2026-07-08T20:32Z
EPSS history
Timeline
  • 08 JUL 20:32Z
    py7zr: O(n^2) algorithmic complexity DoS in PackInfo._read()
    cvelistv5