py7zr: O(n^2) algorithmic complexity DoS in PackInfo._read()
Priority HIGH 77CWE-407Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- None
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Fixed
Attack profile from CVSS 4.0 · CNA. Fix status from CNA and GitHub. Impact type from CWE-407.
Summary
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.
Why it matters now
Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00266 18th percentileScored 2026-11-07
Fix Fixed py7zr (miurahr): 1.1.3py7zr (PyPI): 1.1.3
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| miurahr | py7zr | before 1.1.3 | 1.1.3 | Patch available | CNA |
| — | py7zr (PyPI) | before 1.1.3 | 1.1.3 | Patch available | GHSA-h4gh-22qq-72r7 |
- py7zr Vendormiurahr Affected before 1.1.3 Fixed in 1.1.3 Patch available CNA
- py7zr (PyPI) Vendor— Affected before 1.1.3 Fixed in 1.1.3 Patch available GHSA-h4gh-22qq-72r7
Remediation
- Fix · CNA py7zr (miurahr) Fixed in 1.1.3
- Fix · GHSA-h4gh-22qq-72r7 py7zr (PyPI) Fixed in 1.1.3 Advisory →
Vendor assessments
Timeline
- 2026-10-02 Threatist record created from CVE-2026-55206
- 2026-10-03 Alias added: GHSA-h4gh-22qq-72r7
References
More miurahr vulnerabilities
- TI-2026-39875 py7zr: Decompression bomb (zip bomb) denial of service via unchecked extraction size CVSS 4.0HIGH 8.7
- TI-2026-19237 py7zr: Arbitrary File Write Vulnerability CVSS 3.1HIGH 8.0
Sources
- CVE-2026-55206 · CVE Program
- CVE-2026-55206 · NVD
- FIRST EPSS
- GHSA-h4gh-22qq-72r7 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-55206 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences