AIKIDO-2026-953111
soupsieve is vulnerable to Regular Expression Denial of Service (ReDoS)
53
Medium Risk
This Affects:
soupsieveTL;DR
The IDENTIFIER and VALUE selector patterns use adjacent quantified character classes that match the same characters, so a long failed character run makes the regex engine backtrack across every split point. An unterminated attribute value or an identifier followed by an invalid character leads to quadratic time matching, so around 8 KB of that input consumes roughly eight seconds of CPU. The patch restructures the identifier pattern to remove the overlap so matching stays linear.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and your application compiles user controlled CSS selectors.
Background info
soupsieve is vulnerable to Regular Expression Denial of Service (ReDoS) in versions 0.0.1 - 2.8.4.
How to fix this
Upgrade the soupsieve library to the patch version.
Are You Affected?
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