Microsoft Security Response Center guidance
Vendor revision: Nov 13, 2026Release Notes
Vulnerability intelligence
CVE-2026-126192 and is rated Medium severity with a CVSS score of 6.3. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.
Release Notes
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.
Source: NVD