GHSA-v245-v573-v5vm: linkify-it: Quadratic-complexity DoS via the `mailto:` validator scan-loop on attacker text

Summary linkify-it's schema-scan loop (.test() / .match(), the documented public API) invokes the mailto: schema validator at every mailto: occurrence in the input text. For each occurrence the validator does text.slice(pos) (an O(n) copy) and runs an email regex whose local-part class src_email_name greedily scans the entire remaining tail (O(n)) before failing. With N mailto: occurrences that is N × O(n) = O(n²). Because linkify-it runs on arbitrary user text (markdown-it feeds it whole documents when linkify:true), an unauthenticated attacker can block the single-threaded event loop for many seconds with a small input. No length bound (unlike an HTTP header). Root cause — index.mjs + lib/re.mjs // index.mjs (mailto validator) — runs at every "mailto:" hit 'mailto:': { validate: function (text, pos, self) { const tail = text.slice(pos) // O(n) copy per hit if (!self.re.mailto) self.re.mailto = new RegExp('^' + self.re.src_email_name + '@' + self.re.src_host_strict, 'i') if (self.re.mailto.test(tail)) { ... } // scans the whole O(n) tail return 0 }} // lib/re.mjs:91-93 — every char of "mailto:" (incl. ':','-',';') is in this class: re.src_email_name = '[\\-;:&=\\+\\$,\\.a-zA-Z0-9_][\\-;:&=\\+\\$,\\"\\.a-zA-Z0-9_]*' The while ((m = re.exec(text)) !== null) { …testSchemaAt… } scan loop calls the validator at each mailto: hit; src_email_name greedily consumes the whole tail (all chars are in its class) then fails for lack of @. http:/https: do NOT blow up — their validator requires the tail to start with //, failing in O(1) per hit. Proof of Concept (confirmed, linkify-it 5.0.1, Node v24) const LinkifyIt = require('linkify-it'); const lf = new LinkifyIt(); lf.match('mailto:'.repeat(48000)); // ~336 KB of "mailto:mailto:…" -> seconds of blocked event loop | input (same bytes) | 56 KB | 112 KB | 224 KB | 336 KB | |---|---:|---:|---:|---:| | mailto: contiguous | 97 ms | 357 ms | 1438 ms | 3272 ms | | mailto: space-separated | 2 ms | 3 ms | 5 ms | 8 ms | | http:// c