CVE-2026-126190

Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 4.0, Soup Sieve repeatedly walks the same ancestors while matching descendant combinators, and each additional descendant combinator raises the polynomial degree of the work on deeply nested attacker-influenced HTML or XML. Applications using selectors such as section div div through select(), select_one(), or Beautiful Soup CSS APIs against untrusted documents can have a worker occupied for seconds or minutes, while trusted-only document processing is not affected. Selectors compiled with NOCACHE continue to use the old uncached behavior. This issue is fixed in version 4.0.

• CWE-407

• https://github.com/facelessuser/soupsieve/commit/ff1a5ce7e5addc31626d7b6053511fecdb4f6320
• https://github.com/facelessuser/soupsieve/pull/351
• https://github.com/facelessuser/soupsieve/releases/tag/4.0
• https://github.com/facelessuser/soupsieve/security/advisories/GHSA-mmhr-3c5m-f64f

Published

Nov 12, 2026

Last Modified

Nov 12, 2026

Status

Awaiting Analysis

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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