{"id":"GHSA-253c-mchw-3w2r","revision":null,"records":[{"revision":"8566c333afb4465bbf6bb43d7a8da182","observedAt":"2026-10-24T13:17:17.793+00:00","statement":{"source":"osv","id":"GHSA-253c-mchw-3w2r","aliases":[],"title":"markdown-it linkify: true has two quadratic paths, so a few hundred KB of markdown blocks the event loop for tens of seconds","description":"## Summary\n\nTwo independent quadratic paths in the `linkify: true` handling. Both are in markdown-it's own code rather than in linkify-it, which stays linear on both payloads.\n\n`src/rules_core/linkify.ts` calls `arrayReplaceAt` once per linkified text token, and that rebuilds the whole `children` array each time. A paragraph of N soft-broken lines is one inline token with about 2N children, so you get N rebuilds over a 2N array. Schema-less emails are what reach it. A `http://` link gets consumed by the inline rule first and never arrives as a text token, so those stay linear.\n\n`src/rules_inline/linkify.ts` runs `state.pending.match(SCHEME_RE)` at every `://` in the source. `state.pending` only gets truncated once a link is actually produced, so an unregistered scheme leaves it growing and every `://` rescans the lot.\n\n## Proof of concept\n\nClean install of 15.0.0 from npm, `new MarkdownIt({ linkify: true }).render(payload)`, Node 24.\n\n| N | 5,000 | 10,000 | 20,000 | 40,000 |\n|---|---|---|---|---|\n| `'a@b.co\\n'.repeat(N)`, 34KB to 273KB | 1.1s | 4.7s | 19.6s | 89s |\n| `'a://'.repeat(N)`, 20KB to 156KB | 0.25s | 0.76s | 3.1s | 15.0s |\n\nDoubling the input roughly quadruples the time in both. With `linkify: false` the same inputs run in 25 to 131ms and stay flat.\n\nControls for the first one, all at N=20000: putting every email in a single text token (`'a@b.co '`) takes 0.59s, one email per paragraph (`'a@b.co\\n\\n'`) takes 0.64s, and soft-broken lines with nothing linkifiable take 42ms. So it needs many children AND many of them linkifying. For the second, replaying just the `SCHEME_RE` calls against the same growing prefixes with no markdown-it involved accounts for 11.7s of the 15s.\n\nOrdinary prose does it too. `'ping a@b.co ok\\n'.repeat(20000)` is 293KB and takes 31s.\n\n## Caveat\n\n`linkify` is off by default, so this only reaches apps that turn it on.\n\n## Impact\n\nAvailability only. A few hundred KB of fairly ordinary markdown pins one core for tens of seconds, and because it's quadratic it degrades quickly with size. Nothing is read, written or executed.","state":0,"publishedAt":"2026-09-29T17:57:56+00:00","modifiedAt":"2026-09-29T18:15:04.6923246+00:00","affected":[{"ecosystem":"npm","name":"markdown-it","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"15.0.0"},{"kind":"fixed","version":"15.0.1"}]}],"versions":["15.0.0"],"rawVersionEvidence":null},{"ecosystem":"npm","name":"markdown-it","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"14.3.1"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V4","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"MODERATE"}],"references":["https://github.com/markdown-it/markdown-it/security/advisories/GHSA-253c-mchw-3w2r","https://github.com/markdown-it/markdown-it/commit/09fa07118dda4c953f058848f53dae88395618ca","https://github.com/markdown-it/markdown-it/commit/aaadcfa6d817b3c5f89afb49d97c7b797a6dd4fd","https://github.com/markdown-it/markdown-it/commit/ad70f6b7cff64bee10e42a774147112480ca0d49","https://github.com/markdown-it/markdown-it"],"sourceUrl":"https://github.com/advisories/GHSA-253c-mchw-3w2r","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-253c-mchw-3w2r","identifiers":["GHSA-253c-mchw-3w2r"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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