From c19413b06003ad793e9571604e21d175325f8d87 Mon Sep 17 00:00:00 2001
From: hong4rc <hong4rc@gmail.com>
Date: Sun, 19 Jul 2026 09:41:20 +0700
Subject: [PATCH] fix: Avoid O(n^2) backtracking in GFM email autolink regexes

---
 src/rules.ts                                  |  4 ++--
 test/specs/redos/quadratic_email_autolink.cjs | 10 ++++++++++
 2 files changed, 12 insertions(+), 2 deletions(-)
 create mode 100644 test/specs/redos/quadratic_email_autolink.cjs

diff --git a/src/rules.ts b/src/rules.ts
index 6c42de3083..eb1b8d367d 100644
--- a/src/rules.ts
+++ b/src/rules.ts
@@ -473,11 +473,11 @@ const inlineGfm: Record<InlineKeys, RegExp> = {
   delRDelim,
   url: edit(/^((?:protocol):\/\/|www\.)(?:[a-zA-Z0-9\-]+\.?)+[^\s<]*|^email/)
     .replace('protocol', _caseInsensitiveProtocol)
-    .replace('email', /[A-Za-z0-9._+-]+(@)[a-zA-Z0-9-_]+(?:\.[a-zA-Z0-9-_]*[a-zA-Z0-9])+(?![-_])/)
+    .replace('email', /[A-Za-z0-9._+-]{1,64}(@)[a-zA-Z0-9-_]+(?:\.[a-zA-Z0-9-_]*[a-zA-Z0-9])+(?![-_])/)
     .getRegex(),
   _backpedal: /(?:[^?!.,:;*_'"~()&]+|\([^)]*\)|&(?![a-zA-Z0-9]+;$)|[?!.,:;*_'"~)]+(?!$))+/,
   del: /^(~~?)(?=[^\s~])((?:\\[\s\S]|[^\\])*?(?:\\[\s\S]|[^\s~\\]))\1(?=[^~]|$)/,
-  text: edit(/^(`+|~+|[^`~])(?:(?=[`~])|(?= {2,}\n)|(?=[a-zA-Z0-9.!#$%&'*+\/=?_`{\|}~-]+@)|[\s\S]*?(?:(?=[\\<!\[`*~_]|\b_|protocol:\/\/|www\.|$)|[^ ](?= {2,}\n)|[^a-zA-Z0-9.!#$%&'*+\/=?_`{\|}~-](?=[a-zA-Z0-9.!#$%&'*+\/=?_`{\|}~-]+@)))/)
+  text: edit(/^(`+|~+|[^`~])(?:(?=[`~])|(?= {2,}\n)|(?=[a-zA-Z0-9.!#$%&'*+\/=?_`{\|}~-]{1,64}@)|[\s\S]*?(?:(?=[\\<!\[`*~_]|\b_|protocol:\/\/|www\.|$)|[^ ](?= {2,}\n)|[^a-zA-Z0-9.!#$%&'*+\/=?_`{\|}~-](?=[a-zA-Z0-9.!#$%&'*+\/=?_`{\|}~-]{1,64}@)))/)
     .replace('protocol', _caseInsensitiveProtocol)
     .getRegex(),
 };
diff --git a/test/specs/redos/quadratic_email_autolink.cjs b/test/specs/redos/quadratic_email_autolink.cjs
new file mode 100644
index 0000000000..83e28f290e
--- /dev/null
+++ b/test/specs/redos/quadratic_email_autolink.cjs
@@ -0,0 +1,10 @@
+module.exports = [
+  {
+    markdown: 'a_'.repeat(50000),
+    html: `<p>${'a_'.repeat(50000)}</p>`,
+  },
+  {
+    markdown: 'a*'.repeat(50000),
+    html: `<p>${'a<em>a</em>'.repeat(25000)}</p>`,
+  },
+];