---
id: CVE-2026-85999
title: Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4
summary: >-
  Soup Sieve is a CSS selector library designed to be used with Beautiful Soup
  4. Prior to 2.9, selector_iter in src/soupsieve/css_parser.py trims the raw
  selector with RE_WS_END, an end-anchored WSC whitespace-and-comment expression
  used …
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'
cwe:
  - CWE-400
  - CWE-1333
vendor: facelessuser
product: soupsieve
affected:
  - soupsieve < 2.9
patched:
  - soupsieve 2.9.0
published: '2026-09-17'
updated: '2026-09-23'
sourceUpdated: '2026-09-23T18:12:04.247'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-85999'
references:
  - url: >-
      https://github.com/facelessuser/soupsieve/commit/cf198fcddc9230f06ed39f974eba0ce076b85cda
    label: security-advisories@github.com
  - url: 'https://github.com/facelessuser/soupsieve/releases/tag/2.9'
    label: security-advisories@github.com
  - url: >-
      https://github.com/facelessuser/soupsieve/security/advisories/GHSA-j934-xhv5-fg8f
    label: security-advisories@github.com
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-85999.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-85999'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-85999'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-85999'
  - url: 'https://github.com/advisories/GHSA-j934-xhv5-fg8f'
  - url: 'https://github.com/facelessuser/soupsieve'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2536116'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
  - ghsa
  - pip
  - osv
  - exploit-available
epss: 0.00609
epssPercentile: 0.46909
aliases:
  - GHSA-j934-xhv5-fg8f
ecosystem: pip
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-22T16:55:16.479978Z'
scores:
  nvd: 5.3
  vendor: 5.9
  cna: 5.3
ingestedAt: '2026-09-17T16:21:47.713Z'
---

## Overview

Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 2.9, selector_iter in src/soupsieve/css_parser.py trims the raw selector with RE_WS_END, an end-anchored WSC whitespace-and-comment expression used with search(), so the regular expression engine retries a greedy scan at every starting offset. An attacker-controlled valid selector containing a long internal whitespace run, or a selector containing a long CSS comment run followed by another token, causes quadratic CPU work before tokenization. User-controlled selectors can reach the path through soupsieve.compile() and BeautifulSoup.select(), while applications using only hard-coded selectors are unaffected. This root cause is separate from the IDENTIFIER and VALUE backtracking vulnerability because the cost occurs in RE_WS_END.search during trimming rather than token matching. The resulting CPU consumption can hold the Python GIL, exhaust workers, and stall a service without causing memory corruption or code execution. The issue is fixed in version 2.9.

## Remediation

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

## Package advisory (CVE-2026-85999)

Affected packages:

- `soupsieve < 2.9.0`

Patched in:

- `soupsieve 2.9.0`

Source: https://github.com/advisories/GHSA-j934-xhv5-fg8f

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Exploit Intelligence, Lightspeed Core, Migration Toolkit for Applications 8, OpenShift Lightspeed, Red Hat Ansible Automation Platform 2, Red Hat OpenShift AI (RHOAI), … · no fix planned: Lightspeed Core, Migration Toolkit for Applications 8, OpenShift Lightspeed, Red Hat Ansible Automation Platform 2, … · updated 2026-09-21 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-85999.json)