PYSEC-2026-2973 py7zr: O(n^2) algorithmic complexity DoS in PackInfo._read()

Summary PackInfo.read uses an On^2 cumulative sum pattern where numstreams is read directly from the archive header. A crafted .7z archive with a large numstreams value causes excessive CPU consumption during SevenZipFile.init — no extraction is needed. A 50 KB archive takes 7 seconds of CPU time...

PT-2026-51098

Name of the Vulnerable Software and Affected Versions py7zr versions prior to 1.1.3 Description A denial of service issue exists where a crafted .7z archive with a large numstreams value causes excessive CPU consumption. This occurs because the PackInfo. read function in archiveinfo.py uses an On...