Live › vulnerability › CVE-2026-104844
Go to dashboardpostcss-selector-parser parses a long flat selector such as repeated class names in quadratic time, so a 400 KB input occupies a thread for about 34 seconds. An attacker who can submit selectors to a parsing service can exhaust CPU and degrade availability.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-26 14:11 UTC, 0h before NVD. All times on this page are UTC.
Only applications that parse attacker-supplied selectors synchronously in a request path are exposed, such as CSS sanitizers, CSS-in-JS services and online playgrounds. Ordinary build-time parsing of trusted source files is not affected.
| Product | Ecosystem | Affected | Fixed in |
|---|---|---|---|
| postcss-selector-parser | npm | >= 7.0.0, < 7.1.6 | 7.1.6 |
| postcss-selector-parser | npm | < 6.1.5 | 6.1.5 |
npm ls postcss-selector-parser to list every installed copy and version.postcss-selector-parser to 7.1.6 on the 7.x line or 6.1.5 on the 6.x line.Each row is the first time that source carried this signal. The analyst’s rows are its own findings.
. and # are not word delimiters in the tokenizer, so a flat selector such as
.a.a.a... reaches splitWord() 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:
uniqs(), the indices.forEach 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 maxNestingDepth 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.
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.
Cap the size of selectors accepted from untrusted sources before parsing.
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