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fix(compiler): prevent ReDoS in ShadowCSS _ruleRe regexp #69827

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fix(compiler): prevent ReDoS in ShadowCSS _ruleRe regexp #69827

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8 changes: 7 additions & 1 deletion packages/compiler/src/shadow_css.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1021,7 +1021,13 @@ const _commentWithHashPlaceHolderRe = new RegExp(COMMENT_PLACEHOLDER, 'g');

const BLOCK_PLACEHOLDER = '%BLOCK%';
const _ruleRe = new RegExp(
`(\\s*(?:${COMMENT_PLACEHOLDER}\\s*)*)([^;\\{\\}]+?)(\\s*)((?:{%BLOCK%}?\\s*;?)|(?:\\s*;))`,
// The lookahead (?=[^;{}]*[;{]) ensures the regex fails fast on malformed CSS
// that lacks a terminator, preventing O(k²) backtracking when many comment
// placeholders are followed by content with no closing `;' or `{'.
// Group 1 uses a flat alternation instead of nested \s* quantifiers.
// Group 2 requires a non-whitespace lead so the boundary with group 1 is
// unambiguous and the engine cannot redistribute spaces between the two groups.
`(?=[^;\{\}]*[;\{])((?:${COMMENT_PLACEHOLDER}|\s)*)([^;\{\}\s][^;\{\}]*?)(\s*)((?:{%BLOCK%}?\s*;?)|(?:\s*;))`,
'g',
);
const CONTENT_PAIRS = new Map([['{', '}']]);
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16 changes: 16 additions & 0 deletions packages/compiler/test/shadow_css/process_rules_spec.ts
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Expand Up @@ -65,4 +65,20 @@ describe('ShadowCss, processRules', () => {
).toEqual('a {b2}');
});
});

describe('ReDoS hardening', () => {
it('should complete in linear time with many comment placeholders and no terminator', () => {
// Regression test for polynomial backtracking in _ruleRe.
// Before the fix, a CSS string with k COMMENT placeholders followed by
// content without a `;' or `{' terminator caused O(k²) backtracking.
// The test verifies that processRules returns promptly; a hanging test
// is the observable symptom of the unfixed regex.
const manyComments = ' /* a comment */ '.repeat(200) + 'unclosed-selector';
const start = Date.now();
processRules(manyComments, (rule) => rule);
const elapsed = Date.now() - start;
// Should complete well under 1 second even with 200 comment tokens.
expect(elapsed).toBeLessThan(1000);
});
});
});
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