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Fencer Intel
medium 5.9

CVE-2026-104844 json

PostCSS: Quadratic complexity in flat selector parsing allows CPU exhaustion

published last mo. modified 14d ago also GHSA-rj75-hqrm-r3gf , EUVD-2026-91741

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 33%
public exploits
0
none known

Summary

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.

Patch / fix

  • npm postcss-selector-parser 6.1.5, 7.1.6
  • git-bug openSUSE Tumbleweed 0.11.0-2.1

opensuse advisories openSUSE-SU-2026:12083-1

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-104844 updated cvss 5.9

postcss-selector-parser: postcss-selector-parser: Denial of Service via crafted CSS selectors

  • Red Hat Hardened Images grafana13.1 13.1.6-0.5.hum1, grafana13.2 13.2.1-0.8.hum1, grafana12.4 12.4.12-0.2.hum1, prometheus3.13 3.13.3-0.2.hum1, opentelemetry-collector 0.162.0-0.1.hum1, opentelemetry-collector-k8s 0.162.0-0.1.hum1, +1 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
last mo.

Exploit prediction

0.39% chance of exploitation in the next 30 days, higher than 33% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
npm postcss-selector-parser
>=7.0.0, <7.1.6
<6.1.5
7.1.6
6.1.5

Affected products

  • postcss postcss-selector-parser

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption
  • CWE-407 Inefficient Algorithmic Complexity

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.