CVE-2026-55206
py7zr: O(n^2) algorithmic complexity DoS in PackInfo._read()
Reported by github_m · Published July 8, 2026
py7zr is fixed in 1.1.3 (PyPI)
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.
Fixed versions
Upgrade to a fixed version or later. Language registries are listed first, then Linux distributions, then vendor products.
| Package | Ecosystem | Fixed in |
|---|---|---|
| py7zr | PyPI | 1.1.3 |
Risk scores
Affected products
| Vendor | Product | Versions |
|---|---|---|
| miurahr | py7zr | < 1.1.3 |
| miurahr | py7zr | 0 |
| PyPI | py7zr | 0 |
Timeline
- Jun 19, 2026 CVE Published
- Jul 9, 2026 Coalition ESS Score
- Jul 9, 2026 Security Advisory
- Aug 7, 2026 EPSS Score (24 in total, the first dated here)
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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
- https://nvd.nist.gov/vuln/detail/CVE-2026-55206 advisory
- https://github.com/advisories/GHSA-h4gh-22qq-72r7 advisory