vulnerability / NVI-00010564 / Revision 1
markdown-it linkify: true has two quadratic paths, so a few hundred KB of markdown blocks the event loop for tens of seconds
GitHub lists this reviewed advisory for markdown-it, markdown-it. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
markdown-it
source listed= 15.0.0
## Summary Two 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. `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. `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. ## Proof of concept Clean install of 15.0.0 from npm, `new MarkdownIt({ linkify: true }).render(payload)`, Node 24. | N | 5,000 | 10,000 | 20,000 | 40,000 | |---|---|---|---|---| | `'a@b.co\n'.repeat(N)`, 34KB to 273KB | 1.1s | 4.7s | 19.6s | 89s | | `'a://'.repeat(N)`, 20KB to 156KB | 0.25s | 0.76s | 3.1s | 15.0s | Doubling the input roughly quadruples the time i
markdown-it
source listed< 14.3.1
## Summary Two 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. `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. `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. ## Proof of concept Clean install of 15.0.0 from npm, `new MarkdownIt({ linkify: true }).render(payload)`, Node 24. | N | 5,000 | 10,000 | 20,000 | 40,000 | |---|---|---|---|---| | `'a@b.co\n'.repeat(N)`, 34KB to 273KB | 1.1s | 4.7s | 19.6s | 89s | | `'a://'.repeat(N)`, 20KB to 156KB | 0.25s | 0.76s | 3.1s | 15.0s | Doubling the input roughly quadruples the time i
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-253c-mchw-3w2r ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
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