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Vulnerabilities

Security fix · CVE-2026-104844

PostCSS: Quadratic complexity in flat selector parsing allows CPU exhaustion

Published Oct 5, 2026 · catalog updated Oct 26, 2026 · PostCSS: Quadratic complexity in

Last checked Oct 27, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-104844. EPSS is 0.39%. Act only if a listed version of PostCSS: Quadratic complexity in is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (PostCSS: Quadratic complexity in).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium5.9
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.39%
Remediation
Advisory link
Affected products
npm postcss-selector-parser

### Impact and are not word delimiters in the tokenizer, so a flat selector such as reaches as a single word token carrying n class or id indexes. Three passes scanned those index arrays linearly for every index, making the parse O(n^2) in the number of indexes rather than in input length: , the loop, and the Sass-interpolation filter. Parsing a 400 KB flat selector took ~34 s on a modern laptop, fully occupying a single thread. A benign selector of identical byte size parses in tens of milliseconds, so the cost is driven by the index count, not the input size. The nesting depth of such a selector is 0, so the guard added in 7.1.3 offers no protection. Reachability is deployment dependent. Only consumers that parse untrusted, attacker-supplied selectors synchronously in a request path are exposed, for example CSS sanitizers, CSS-in-JS services and online playgrounds. Ordinary build-time use on trusted sources is not affected. ### Patches Fixed in 7.1.6. The three passes now use Set membership tests, making parsing linear in the number of indexes. There is no behaviour change: parsing is byte-identical on a differential corpus of 8413 selectors. ### Workarounds Cap the size of selectors accepted from untrusted sources before parsing.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • npm postcss-selector-parser0 → 6.1.5
  • npm postcss-selector-parser7.0.0 → 7.1.6

How to fix CVE-2026-104844

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-104844. EPSS is 0.39%. Act only if a listed version of PostCSS: Quadratic complexity in is installed.

Which versions are affected?

Compare what you have installed with 0 → 6.1.5, 7.0.0 → 7.1.6. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-400: Uncontrolled Resource Consumption; CWE-407. EPSS 0.39%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 5, 2026 · GitHub Advisory Database

    Detected

    ### Impact and are not word delimiters in the tokenizer, so a flat selector such as reaches as a single word token carrying n class or id indexes. Three passes scanned those index arrays linearly for every index, making the parse O(n^2) in the number of indexes rather than in input length: , the loop, and the Sass-interpolation filter. Parsing a 400 KB flat selector took ~34 s on a modern laptop,

  2. Oct 26, 2026 · GitHub Advisory Database

    Fix available

    postcss-selector-parser fixed in 7.1.6; postcss-selector-parser fixed in 6.1.5

  3. Oct 26, 2026 · GitHub Advisory Database

    Fix available

    postcss-selector-parser fixed in 7.1.6

  4. Oct 26, 2026 · GitHub Advisory Database

    Fix available

    postcss-selector-parser fixed in 6.1.5

  5. Oct 26, 2026 · GitHub Advisory Database

    Updated

    ### Impact and are not word delimiters in the tokenizer, so a flat selector such as reaches as a single word token carrying n class or id indexes. Three passes scanned those index arrays linearly for every index, making the parse O(n^2) in the number of indexes rather than in input length: , the loop, and the Sass-interpolation filter. Parsing a 400 KB flat selector took ~34 s on a modern laptop,

Sources

References

Freshness

Last verified in this catalog Oct 26, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • CVE.orgOct 27, 2026
  • GitHub Advisory DatabaseOct 26, 2026
  • OpenSSF OSV / OSV ScannerOct 26, 2026