PostCSS: Quadratic complexity in flat selector parsing allows CPU exhaustion (CVE-2026-104844)

What is affected, what to do

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.

Update Postcss-selector-parser to version 7.1.6.

Affected

• Postcss-selector-parser lt *..7.1.6

Fixed in

• Postcss-selector-parser 7.1.6

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Metrics

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2

NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

Read in glossary

Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.

CRA

The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

Read in glossary

From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.

ISO/IEC 27001

ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

Read in glossary

Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

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.

Source: OSV (Open Source Vulnerabilities), GitHub Security Advisories, NVD (NIST), cvelistv5

Vendors and products

• Postcss

Weakness classes (CWE)

• CWE-400Uncontrolled Resource Consumption

  Class

  The product does not properly control the allocation and maintenance of a limited resource.

  Entry at MITRE CWE-400

• CWE-407Inefficient Algorithmic Complexity

  Class

  An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.

  Entry at MITRE CWE-407

References & sources

• github.compostcss/postcss-selector-parser/security/advisories/GHSA-rj75-h…x_refsource_CONFIRM, web
• github.compostcss/postcss-selector-parser/commit/62b191792df0a0bc56062e5a…x_refsource_MISC, web
• github.compostcss/postcss-selector-parser/releases/tag/7.1.6x_refsource_MISC, web
• NVD (NIST)vuln/detail/CVE-2026-104844advisory
• github.compostcss/postcss-selector-parserpackage
• github.compostcss/postcss-selector-parser/pull/346web
• github.compostcss/postcss-selector-parser/commit/70b0779c843462197380d25d…web
• github.compostcss/postcss-selector-parser/releases/tag/6.1.5web

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

1. 02.10.2026Record modifiedCISA ADP

   CISA assessment (SSVC): exploitation: none known, automatable: no

   Show the original change

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   SSVC assessment	added	—	{"id":"CVE-2026-104844","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-02T16:16:26.803770Z"}

   Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

2. 02.10.2026ReceivedGitHub

   CVSS V3.1: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

   Weakness type: CWE-407, CWE-400

   Description added or changed

   New references:

   • https://github.com/postcss/postcss-selector-parser/commit/62b191792df0a0bc56062e5a875bc74aae2a51cd
   • https://github.com/postcss/postcss-selector-parser/releases/tag/7.1.6
   • https://github.com/postcss/postcss-selector-parser/security/advisories/GHSA-rj75-hqrm-r3gf
   Show 8 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Description	added	—	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.
   CVSS	added	—	AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
   Weakness type (CWE)	added	—	CWE-407
   Weakness type (CWE)	added	—	CWE-400
   Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/104xxx/CVE-2026-104844.json">CVE-2026-104844</a>
   Reference	added	—	https://github.com/postcss/postcss-selector-parser/commit/62b191792df0a0bc56062e5a875bc74aae2a51cd
   Reference	added	—	https://github.com/postcss/postcss-selector-parser/releases/tag/7.1.6
   Reference	added	—	https://github.com/postcss/postcss-selector-parser/security/advisories/GHSA-rj75-hqrm-r3gf

   Source identifier: security-advisories@github.com