CVE-2026-126192

Soup Sieve: General sibling combinator inside :has() matches untrusted HTML in quadratic time

publishedCWE-400CWE-407

Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 2.10, matching a developer-authored selector that places the general sibling combinator inside :has() repeatedly scans each candidate element's following siblings when the right-hand side is absent, producing quadratic work on attacker-controlled HTML. Applications that evaluate a fixed selector such as div:has(a ~ b) over untrusted markup can have a worker occupied for minutes by a small document, while the adjacent sibling form and trusted-only document processing are not affected in the same way. This issue is fixed in version 2.10.

Technical severity6.3 mediumCVSS 4.0 · CNA: GitHub_M

Published2026-11-12Source updated 2026-11-13

Collected2026-11-133 attributed sources

Fixes and workarounds

Fix

soupsieve (PyPI): OSV reports a fixed version 2.10.0. Check the advisory for supported release branches.

Source: OSV GHSA-4j63-6c4x-wfg4

Affected products and versions

Affected products, source version ranges and reporting authorities
Product	Versions	Authority
soupsieve facelessuser	< 2.10 (affected)	CNA: GitHub_M
soupsieve `soupsieve` PyPI	0.4 (affected, PyPI) 0.5 (affected, PyPI) 0.5.1 (affected, PyPI) 0.5.2 (affected, PyPI) 0.5.3 (affected, PyPI) 0.6 (affected, PyPI) 1.0 (affected, PyPI) 1.0.1 (affected, PyPI) 1.0.2 (affected, PyPI) 1.0b1 (affected, PyPI) 1.0b2 (affected, PyPI) 1.1 (affected, PyPI) 1.2 (affected, PyPI) 1.2.1 (affected, PyPI) 1.3 (affected, PyPI) 1.3.1 (affected, PyPI) 1.4 (affected, PyPI) 1.5 (affected, PyPI) 1.6 (affected, PyPI) 1.6.1 (affected, PyPI) 1.6.2 (affected, PyPI) 1.7 (affected, PyPI) 1.7.1 (affected, PyPI) 1.7.2 (affected, PyPI) 1.7.3 (affected, PyPI) 1.8 (affected, PyPI) 1.9 (affected, PyPI) 1.9.1 (affected, PyPI) 1.9.2 (affected, PyPI) 1.9.3 (affected, PyPI) 1.9.4 (affected, PyPI) 1.9.5 (affected, PyPI) 1.9.6 (affected, PyPI) 2.0 (affected, PyPI) 2.0.1 (affected, PyPI) 2.1 (affected, PyPI) 2.2 (affected, PyPI) 2.2.1 (affected, PyPI) 2.3 (affected, PyPI) 2.3.1 (affected, PyPI) 2.3.2 (affected, PyPI) 2.3.2.post1 (affected, PyPI) 2.4 (affected, PyPI) 2.4.1 (affected, PyPI) 2.5 (affected, PyPI) 2.6 (affected, PyPI) 2.7 (affected, PyPI) 2.8 (affected, PyPI) 2.8.1 (affected, PyPI) 2.8.2 (affected, PyPI) 2.8.3 (affected, PyPI) 2.8.4 (affected, PyPI) 2.9 (affected, PyPI) 2.9.1 (affected, PyPI) 2.9.2 (affected, PyPI) Ecosystem version events: introduced 0; fixed 2.10.0 Source events (ECOSYSTEM) `[ { "introduced": "0" }, { "fixed": "2.10.0" } ]` Other versions: unaffected	OSV GHSA-4j63-6c4x-wfg4

Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.

CVSS assessments

CVSS scores, vectors and reporting authorities
Version / score	Vector	Authority
4.0 / 6.3 medium	`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N`	CNA: GitHub_M
4.0 / 6.3 medium	`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X`	NVD: [email protected]

Exploit evidence

https://github.com/facelessuser/soupsieve/security/advisories/GHSA-4j63-6c4x-wfg4
exploit · ADP: CISA-ADP

References

https://github.com/facelessuser/soupsieve/security/advisories/GHSA-4j63-6c4x-wfg4CNA: GitHub_M · x_refsource_CONFIRM
https://github.com/facelessuser/soupsieve/pull/304CNA: GitHub_M · x_refsource_MISC
https://github.com/facelessuser/soupsieve/commit/ffb88cca745c591224f74a8e86414a85e8f35fc0CNA: GitHub_M · x_refsource_MISC
https://github.com/facelessuser/soupsieve/releases/tag/2.10CNA: GitHub_M · x_refsource_MISC
https://github.com/facelessuser/soupsieve/security/advisories/GHSA-4j63-6c4x-wfg4ADP: CISA-ADP · exploit
https://github.com/facelessuser/soupsieve/commit/ffb88cca745c591224f74a8e86414a85e8f35fc0[email protected]
https://github.com/facelessuser/soupsieve/pull/304[email protected]
https://github.com/facelessuser/soupsieve/releases/tag/2.10[email protected]
https://github.com/facelessuser/soupsieve/security/advisories/GHSA-4j63-6c4x-wfg4[email protected]
https://github.com/advisories/GHSA-4j63-6c4x-wfg4OSV / GitHub Security Advisories · advisory
https://osv.dev/vulnerability/GHSA-4j63-6c4x-wfg4OSV / GitHub Security Advisories · osv

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