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Advisory record · GHSA-h4gh-22qq-72r7

py7zr: O(n^2) algorithmic complexity DoS in PackInfo._read()

CVSS 8.7 HighEPSS 0.0027 · 18th percentile

Published by the GitHub Advisory Database at 19 Jun 2026, 21:16 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
py7zrPyPI<1.1.31.1.3
Identifiers
GHSA-h4gh-22qq-72r7 · CVE-2026-55206 · PYSEC-2026-2973
Weakness (CWE)
CWE-407
Tags
Published
19 Jun 2026
Updated
13 Jul 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

The py7zr package, versions before 1.1.3, has a quadratic-complexity flaw in how it parses the packed-stream information in a .7z archive header. An attacker who can get an application to open a crafted .7z archive from an untrusted source can make it consume a large amount of CPU time, with a 50 KB archive reported to take about 7 seconds, during SevenZipFile() initialization before any extraction. Upgrade to py7zr 1.1.3 or later.

Written 6 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
8.7 High 4.0 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 CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0027, the 18th percentile, on 15 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 15:01 UTC First seen by agentprime
  2. 31 Oct 2026, 15:01 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.