Vulnerability · Published Jul 8, 2026 · Assigned by GitHub_M
CVE-2026-55206py7zr: O(n^2) algorithmic complexity DoS in PackInfo._read()
High 8.7
In plain English
A high-severity security flaw in py7zr from miurahr. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 19% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | py7zr | no fix listed | DEBIAN-CVE-2026-55206 |
| Debian:13 | py7zr | no fix listed | DEBIAN-CVE-2026-55206 |
| Debian:14 | py7zr | 1.1.3+dfsg-1 | DEBIAN-CVE-2026-55206 |
| PyPI | py7zr | 1.1.3 | GHSA-h4gh-22qq-72r7 |
| PyPI | py7zr | 1.1.3 | PYSEC-2026-2973 |
| Ubuntu:22.04:LTS | py7zr | no fix listed | UBUNTU-CVE-2026-55206 |
| Ubuntu:24.04:LTS | py7zr | no fix listed | UBUNTU-CVE-2026-55206 |
| Ubuntu:25.10 | py7zr | no fix listed | UBUNTU-CVE-2026-55206 |
| Ubuntu:26.04:LTS | py7zr | no fix listed | UBUNTU-CVE-2026-55206 |
| Ubuntu:26.10 | py7zr | no fix listed | UBUNTU-CVE-2026-55206 |
Affected products (as reported)
Weakness: CWE-407 · 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
References
- https://github.com/miurahr/py7zr/security/advisories/GHSA-h4gh-22qq-72r7 x_refsource_CONFIRM
- https://github.com/miurahr/py7zr/commit/d7aa3a197d15c75a65b24f796d3a69f83806d3f8 x_refsource_MISC
- https://github.com/miurahr/py7zr/releases/tag/v1.1.3 x_refsource_MISC