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security: cap text-level CSS parser recursion/output on calc(), :not(), :is() - #273
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calcParser's grammar (expr/term/factor, the standard mutually-
recursive expression-parser shape) recurses from factor straight
back into expr for each '(' with no depth check. Unlike deep HTML
element nesting, nothing upstream bounds how many parens a single
calc(...) value's own source text can carry -- a style="..."
attribute on the main document (capped only at 32MB) can trivially
carry millions.
Confirmed live: a synthetic 3,000,000-deep calc((((...1...))))
crashes with an unrecoverable "fatal error: stack overflow" (not a
panic -- recover() cannot catch it) where 1,000,000 does not yet.
factor now caps its own recursion at 256 levels, failing the same
way this parser already fails on any other malformed input rather
than recursing further.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
tannevaled
changed the title
This was referenced Oct 11, 2026
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Summary
calcParser's grammar (expr/term/factor, the standard mutually-recursive expression-parser shape) recurses fromfactorstraight back intoexprfor each(with no depth check.calc(...)value's own source text can carry — astyle="..."attribute on the main document (capped only at 32MB) can trivially carry millions.calc((((...1...))))crashes with an unrecoverablefatal error: stack overflow(not a panic —recover()cannot catch it) where 1,000,000 does not yet.factornow caps its own recursion at 256 levels, failing the same way this parser already fails on any other malformed input rather than recursing further.Test plan
go build ./...go test ./...(all packages pass)TestResolveCalcDoesNotCrashOnPathologicallyDeepParenscsspackage coverage unaffected (99.5% before/after);factor's own coverage rises slightly (92.0%→95.0%)🤖 Generated with Claude Code