CVE-2026-55206
HighCVSS 8.7Exploitation Probability (EPSS)
Low risk24th percentile - higher than 24% of all known CVEs
Summary
The py7zr library prior to version 1.1.3 contains a denial-of-service vulnerability causing excessive CPU consumption during SevenZipFile initialization. The PackInfo._read() function in archiveinfo.py uses an O(n^2) cumulative sum pattern for attacker-controlled numstreams values parsed from archive headers, allowing a crafted .7z archive to trigger CPU exhaustion.
Risk Assessment
An attacker can supply a specially crafted .7z archive that, when opened or extracted, causes significant CPU load, leading to a denial of service (DoS) for applications using py7zr.
Recommendation
Immediately update the py7zr library to version 1.1.3 or later, which contains the fix for this vulnerability.
Other vulnerabilities in py7zr
See all- CVE-2026-55195High
The py7zr library before version 1.1.3 does not track the total decompressed size, allowing a decompression bomb attack. A crafted .7z file (e.g., 15.6 KB) can expand to 100 MB, exhausting disk space or memory.
- CVE-2026-23879High
The py7zr library, used for compressing and decompressing 7zip archives, contains an arbitrary file write vulnerability in versions 1.1.2 and below. This allows attackers to create malicious archives that can restore symbolic links to arbitrary directories in the file system.
Original NVD description (English source)
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.