vulnerability / NVI-00018316 / Revision 1
markdown-it: Quadratic complexity DoS in smartquotes rule via replaceAt string operations
GitHub lists this reviewed advisory for 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
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5.3 medium
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
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<= 14.1.1
### Summary A quadratic time complexity vulnerability exists in markdown-it's smartquotes rule (enabled via the `typographer: true` option). An attacker can craft a markdown input consisting of consecutive quotation marks that causes the parser to consume excessive CPU time, leading to denial of service. ### Details The vulnerability is in the `replaceAt()` helper function used by the smartquotes rule in `lib/rules_core/smartquotes.mjs`: ```javascript function replaceAt (str, index, ch) { return str.slice(0, index) + ch + str.slice(index + 1) } ``` When markdown-it processes a text token containing many quotation marks (either `"` or `'`) with `typographer: true`, the smartquotes rule iterates through each quote character and calls `replaceAt()` to substitute it with a typographic (curly) quote. Each call to `replaceAt()` creates three new string slices and concatenates them, which is an O(n) operation where n is the length of the string. Since this is called once per quote character in the token, and there are n quote characters, the total time complexity becomes O(n^2). The root cause is that the smartquotes rule modifies `token.content` in place using string slicing rat
03 / Response
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04 / Limits
What this report cannot establish
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05 / Provenance
Sources you can inspect
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- GHSA-6v5v-wf23-fmfq ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
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