# CVE-2026-126191: Soup Sieve: Exponential ReDoS in selector compilation via \9-run in CSS_ESCAPES/IDENTIFIER

Status: published. Published: 2026-11-12. Updated: 2026-11-12.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- facelessuser / soupsieve: < 3.0 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: CNA: GitHub_M

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: NVD: security-advisories@github.com

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-1333

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/facelessuser/soupsieve/security/advisories/GHSA-6655-6qjp-jx7x (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/facelessuser/soupsieve/pull/300 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/facelessuser/soupsieve/commit/dbfa2854ff31a863326bd6660d4e55c6f068db9e (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/facelessuser/soupsieve/releases/tag/3.0 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/facelessuser/soupsieve/commit/dbfa2854ff31a863326bd6660d4e55c6f068db9e (security-advisories@github.com)

- https://github.com/facelessuser/soupsieve/pull/300 (security-advisories@github.com)

- https://github.com/facelessuser/soupsieve/releases/tag/3.0 (security-advisories@github.com)

- https://github.com/facelessuser/soupsieve/security/advisories/GHSA-6655-6qjp-jx7x (security-advisories@github.com)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-126191; retrieved 2026-11-12; source updated 2026-11-12

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126191; retrieved 2026-11-12; source updated 2026-11-12

Revision: 19a861ed0c7551309e7b8073504270eb30ef4f3b1dfd0d70d2746b3f9a78862e

Canonical: https://y2.dev/cve/CVE-2026-126191

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