PostCSS: Quadratic complexity in flat selector parsing allows CPU exhaustion

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-104844
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-02 16:16:46 UTC
Updated2026-10-02 18:44:11 UTC
DescriptionPostCSS 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.

Risk And Classification

Primary CVSS: v3.1 5.9 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Problem Types: CWE-400 | CWE-407 | CWE-400 CWE-400: Uncontrolled Resource Consumption | CWE-407 CWE-407: Inefficient Algorithmic Complexity

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.9MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED5.9MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Postcss Postcss-selector-parser affected < 7.1.6 Not specified

References

ReferenceSourceLinkTags
github.com/postcss/postcss-selector-parser/security/advisories/GHSA-rj75... [email protected] github.com
github.com/postcss/postcss-selector-parser/commit/62b191792df0a0bc56062e... [email protected] github.com
github.com/postcss/postcss-selector-parser/releases/tag/7.1.6 [email protected] github.com
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