fix: anchor keyValuePairsReg to prevent quadratic backtracking#6558
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fix: anchor keyValuePairsReg to prevent quadratic backtracking#6558
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The content-type parameter regex was vulnerable to O(N²) backtracking on malformed input without `=` characters. Adding a `(^|;)` anchor ensures the engine only attempts matches at parameter boundaries, reducing worst-case complexity to O(N) with no measurable impact on valid input throughput.
Fdawgs
reviewed
Mar 6, 2026
jsumners
reviewed
Mar 6, 2026
Address review feedback: use (?:^|;) non-capture group to keep original match indices. Remove benchmark file and tinybench dependency.
jsumners
approved these changes
Mar 6, 2026
Fdawgs
reviewed
Mar 6, 2026
Co-authored-by: Frazer Smith <[email protected]> Signed-off-by: Manuel Spigolon <[email protected]>
Eomm
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Mar 7, 2026
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Size Time(ms) Ratio vs prev
1000 0.1 -
2000 0.0 0.31
5000 0.0 1.86
10000 0.1 2.01
20000 0.1 1.97
50000 0.3 2.47
Fdawgs
approved these changes
Mar 7, 2026
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Summary
/([\w!#$%&'*+.^|~-]+)=([^;])/gmexhibited O(N²) backtracking on malformed input (e.g. long strings without=). Adding a(^|;)\sanchor ensures the engine only attempts matches at parameter boundaries (^or;`), reducing worst-case complexity to O(N).benchmarks/content-type.js— no measurable throughput difference on valid inputs.Test plan
content-type.test.jstests pass