PostCSS Selector Parser up to 7.1.5 Split Word src/parser.js splitWord improper synchronization

Summaryinfo

A vulnerability marked as problematic has been reported in PostCSS Selector Parser up to 7.1.5. Impacted is the function splitWord of the file src/parser.js of the component Split Word. The manipulation leads to improper synchronization. This vulnerability is referenced as CVE-2026-104844. Remote exploitation of the attack is possible. No exploit is available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in PostCSS Selector Parser up to 7.1.5. This issue affects the function splitWord of the file src/parser.js of the component Split Word. The manipulation with an unknown input leads to a improper synchronization vulnerability. Using CWE to declare the problem leads to CWE-662. The product utilizes multiple threads or processes to allow temporary access to a shared resource that can only be exclusive to one process at a time, but it does not properly synchronize these actions, which might cause simultaneous accesses of this resource by multiple threads or processes. Impacted is availability. The summary by CVE is:

PostCSS Selector Parser is a CSS selector parser that integrates with PostCSS but does not require it. Prior to 7.1.6, src/parser.js splitWord() can receive a flat selector as one word token carrying many class or ID indexes because period and hash characters are not tokenizer word delimiters. The uniqs() deduplication and per-index class and ID membership checks repeatedly scan the class and ID index arrays, while a separate Sass-interpolation filtering pass also performs repeated linear scanning. Together, these passes make parsing quadratic in the number of indexes and allow a crafted selector to occupy a synchronous parser thread. The maxNestingDepth guard does not mitigate the issue because the hostile selector can have zero nesting depth. Only consumers that synchronously parse untrusted selectors in an exposed request path are affected; ordinary build-time parsing of trusted sources is not affected. This issue is fixed in version 7.1.6.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-104844 since 10/02/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available.

Upgrading to version 7.1.6 eliminates this vulnerability.

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Productinfo

Vendor

• PostCSS

Name

• Selector Parser

Version

• 7.1.0
• 7.1.1
• 7.1.2
• 7.1.3
• 7.1.4
• 7.1.5

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CPE 2.2info

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