---
id: CVE-2026-126191
title: >-
  Soup Sieve: Exponential ReDoS in selector compilation via \9-run in
  CSS_ESCAPES/IDENTIFIER
summary: >-
  Soup Sieve is a CSS selector library designed to be used with Beautiful Soup
  4. Prior to 3.0, the CSS_ESCAPES and IDENTIFIER regular-expression subpatterns
  can backtrack exponentially on runs of ambiguous digit escapes in an
  attribute-na…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: cna
cwe:
  - CWE-1333
vendor: facelessuser
product: soupsieve
affected:
  - soupsieve < 3.0
published: '2026-11-12'
updated: '2026-11-12'
sourceUpdated: '2026-11-12T16:57:01.566Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-126191'
references:
  - url: >-
      https://github.com/facelessuser/soupsieve/security/advisories/GHSA-6655-6qjp-jx7x
    label: >-
      https://github.com/facelessuser/soupsieve/security/advisories/GHSA-6655-6qjp-jx7x
  - url: 'https://github.com/facelessuser/soupsieve/pull/300'
    label: 'https://github.com/facelessuser/soupsieve/pull/300'
  - url: >-
      https://github.com/facelessuser/soupsieve/commit/dbfa2854ff31a863326bd6660d4e55c6f068db9e
    label: >-
      https://github.com/facelessuser/soupsieve/commit/dbfa2854ff31a863326bd6660d4e55c6f068db9e
  - url: 'https://github.com/facelessuser/soupsieve/releases/tag/3.0'
    label: 'https://github.com/facelessuser/soupsieve/releases/tag/3.0'
tags:
  - cve.org
ingestedAt: '2026-11-12T17:51:14.505Z'
---

## Overview

Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 3.0, the CSS_ESCAPES and IDENTIFIER regular-expression subpatterns can backtrack exponentially on runs of ambiguous digit escapes in an attribute-name or tag position of an otherwise valid selector. The failure occurs during selector compilation through soupsieve.compile() or Beautiful Soup select() before SELECTOR_LIMIT is applied, so an application that accepts untrusted selector strings can have a worker stalled by a short input. This issue is fixed in version 3.0.

## Affected

- `soupsieve < 3.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.