CVE-2026-126189
Published:November 12, 2026
Updated:November 13, 2026
Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 4.0.1, Soup Sieve repeatedly searches descendant subtrees for each candidate evaluated by :has() and repeatedly reevaluates a parent containing :has(> ...) for each child, causing quadratic matching on deeply nested or wide attacker-influenced HTML or XML. Applications using ordinary fixed selectors through select(), select_one(), or Beautiful Soup CSS APIs against untrusted documents can have a worker occupied for seconds or minutes, while applications that process only trusted documents are not affected. Selectors compiled with NOCACHE continue to use the old uncached behavior. This issue is fixed in version 4.0.1.
Affected Packages
soupsieve (CONDA):
Affected version(s) >=3.0 <4.0.1 || =4.0 <4.0.1 || >=1.6.2 <4.0.1 || >=2.0.1 <4.0.1Fix Suggestion:
Update to version 4.0.1https://github.com/facelessuser/soupsieve.git (GITHUB):
Affected version(s) >=0.4.0 <4.0.1 || >=1.0.0b1 <4.0.1 || >=2.0.0 <4.0.1 || >=3.0 <4.0.1 || =4.0 <4.0.1Fix Suggestion:
Update to version 4.0.1soupsieve (PYTHON):
Affected version(s) >=0.4 <4.0.1 || >=1.0b1 <4.0.1 || >=3.0 <4.0.1 || =4.0 <4.0.1 || >=2.0 <4.0.1Fix Suggestion:
Update to version 4.0.1Related Resources (7)
Do you need more information?
Contact UsCVSS v4
Base Score:
6.9
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
LOW
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
5.3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
LOW
Weakness Type (CWE)
Inefficient Algorithmic Complexity
EPSS
Base Score:
0.30