Quality: Potential ReDoS vulnerability in regex-based CSS function parsing#627
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In `lib/variables.js`, the `replaceVariables` function uses a regex `/([a-z\-]+)\s*\(\s*([^\(\)]*?)\s*(?:,\s*([^\(\)]*?)\s*)?\s*\)/i` to parse CSS function calls. This regex contains nested quantifiers and backreferences that could be exploited with maliciously crafted CSS input, causing catastrophic backtracking and denial of service. The regex is applied in a `while` loop with `exec`, compounding the risk. The `[^\(\)]*?` pattern with the surrounding optional groups creates multiple paths for exponential backtracking when encountering nested or malformed parentheses. Signed-off-by: tomaioo <203048277+tomaioo@users.noreply.github.com>
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Summary
Quality: Potential ReDoS vulnerability in regex-based CSS function parsing
Problem
Severity:
High| File:lib/variables.js:L12In
lib/variables.js, thereplaceVariablesfunction uses a regex/([a-z\-]+)\s*\(\s*([^\(\)]*?)\s*(?:,\s*([^\(\)]*?)\s*)?\s*\)/ito parse CSS function calls. This regex contains nested quantifiers and backreferences that could be exploited with maliciously crafted CSS input, causing catastrophic backtracking and denial of service. The regex is applied in awhileloop withexec, compounding the risk. The[^\(\)]*?pattern with the surrounding optional groups creates multiple paths for exponential backtracking when encountering nested or malformed parentheses.Solution
Replace the hand-rolled regex parser with a proper CSS value tokenizer, or at minimum add input length limits and timeout protection. Consider using a well-tested CSS parsing library instead of regex for this task. If regex must be used, simplify the pattern to avoid nested quantifiers and test with ReDoS detection tools.
Changes
lib/variables.js(modified)