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Advisory record · GHSA-gjv8-xp57-g29c

Soup Sieve: Polynomial-time ReDoS (O(n²)) in the `IDENTIFIER` / `VALUE` selector sub-patterns

CVSS 5.3 MediumEPSS 0.0061 · 49th percentile

Published by the GitHub Advisory Database at 17 Sept 2026, 20:32 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
soupsievePyPI<2.9.02.9.0
Identifiers
GHSA-gjv8-xp57-g29c · CVE-2026-86000 · PYSEC-2026-4170
Weakness (CWE)
CWE-400 · CWE-1333
Tags
Published
17 Sept 2026
Updated
1 Oct 2026

Machine-written summary

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

Soup Sieve versions before 2.9.0 are vulnerable to a denial-of-service issue in how selector strings are parsed. A long identifier or attribute value in a CSS selector that ends in a failed match can cause parsing time to grow quadratically, so a few kilobytes of selector can stall the process for seconds. An attacker needs to supply the selector, which applications do when they pass user-controlled selectors to BeautifulSoup's select methods. Upgrade to soupsieve 2.9.0 or later. Limiting selector length before passing it to the library is an additional safeguard.

Written 1 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
5.3 Medium 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0061, the 49th percentile, on 13 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:09 UTC First seen by agentprime
  2. 31 Oct 2026, 14:09 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.