facelessuser Soup Sieve up to 2.8 CSS Parser css_parser.py selector_iter incorrect regex

Summaryinfo

A vulnerability classified as problematic was found in facelessuser Soup Sieve up to 2.8. Affected is the function selector_iter of the file src/soupsieve/css_parser.py of the component CSS Parser. Executing a manipulation can lead to incorrect regex. The identification of this vulnerability is CVE-2026-85999. The attack may be launched remotely. There is no exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability classified as problematic was found in facelessuser Soup Sieve up to 2.8. This vulnerability affects the function selector_iter of the file src/soupsieve/css_parser.py of the component CSS Parser. The manipulation with an unknown input leads to a incorrect regex vulnerability. The CWE definition for the vulnerability is CWE-185. The product specifies a regular expression in a way that causes data to be improperly matched or compared. As an impact it is known to affect availability. CVE summarizes:

Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 2.9, selector_iter in src/soupsieve/css_parser.py trims the raw selector with RE_WS_END, an end-anchored WSC whitespace-and-comment expression used with search(), so the regular expression engine retries a greedy scan at every starting offset. An attacker-controlled valid selector containing a long internal whitespace run, or a selector containing a long CSS comment run followed by another token, causes quadratic CPU work before tokenization. User-controlled selectors can reach the path through soupsieve.compile() and BeautifulSoup.select(), while applications using only hard-coded selectors are unaffected. This root cause is separate from the IDENTIFIER and VALUE backtracking vulnerability because the cost occurs in RE_WS_END.search during trimming rather than token matching. The resulting CPU consumption can hold the Python GIL, exhaust workers, and stall a service without causing memory corruption or code execution. The issue is fixed in version 2.9.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-85999 since 09/04/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available.

Upgrading to version 2.9 eliminates this vulnerability.

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Productinfo

Vendor

• facelessuser

Name

• Soup Sieve

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6
• 2.7
• 2.8

CPE 2.3info

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CPE 2.2info

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