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Advisory record · GHSA-j934-xhv5-fg8f

Soup Sieve: Polynomial-time ReDoS (O(n²)) in the whitespace/comment trimming regex `RE_WS_END` (triggers on VALID selectors)

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-j934-xhv5-fg8f · CVE-2026-85999 · PYSEC-2026-4171
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.

Soupsieve versions before 2.9.0 are vulnerable to a denial of service: a long run of whitespace or CSS comments inside an otherwise valid selector makes compilation take quadratic time. An attacker who can supply a CSS selector to an application using soupsieve or BeautifulSoup's select methods can stall the process, with a 20 KB selector taking about 10 seconds of CPU. Upgrade to soupsieve 2.9.0 or later. The source gives no workaround beyond capping selector length before compiling.

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.