Fix LinkifyIt match detection

Author: theinfosecguy

javascript/ql/lib/change-notes/2026-09-15-linkify-it-match.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Calls to `LinkifyIt.match()` are no longer incorrectly identified as regular expression operations.

javascript/ql/lib/semmle/javascript/Regexp.qll

@@ -986,6 +986,22 @@ private predicate isMatchObjectProperty(string name) {
   name in ["length", "index", "input", "groups"]
 }
 
+/** Gets an API node representing a `LinkifyIt` instance. */
+private API::Node linkifyItInstance() {
+  result = API::moduleImport("linkify-it").getMember("exports").getMember("LinkifyIt").getInstance()
+  or
+  result = API::moduleImport("linkify-it").getMember("LinkifyIt").getInstance()
+  or
+  result = API::moduleImport("linkify-it").getMember("exports").getMember("linkifyit").getReturn()
+  or
+  result = API::moduleImport("linkify-it").getMember("linkifyit").getReturn()
+  or
+  // Before version 6, the module export was the factory function.
+  result = API::moduleImport("linkify-it").getReturn()
+  or
+  result = linkifyItInstance().getMember(["add", "set", "tlds"]).getReturn()
+}
+
 /** Holds if `call` is a call to `match` whose result is used in a way that is incompatible with Match objects. */
 overlay[global]
 private predicate isUsedAsNonMatchObject(DataFlow::MethodCallNode call) {
@@ -1006,6 +1022,8 @@ private predicate isUsedAsNonMatchObject(DataFlow::MethodCallNode call) {
     call.asExpr() = any(ExprStmt stmt).getExpr()
     or
     call = API::moduleImport("sinon").getMember("match").getACall()
+    or
+    call = linkifyItInstance().getMember("match").getACall()
   )
 }
 

javascript/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegExp/IncompleteHostnameRegExp.expected

@@ -1,3 +1,4 @@
+| linkify-it/tst-LinkifyIt.js:21:25:21:48 | ^https://www.example.com | This regular expression has an unescaped '.' before 'example.com', so it might match more hosts than expected. | linkify-it/tst-LinkifyIt.js:21:24:21:49 | "^https ... le.com" | here |
 | tst-IncompleteHostnameRegExp.js:3:3:3:28 | ^http:\\/\\/test.example.com | This regular expression has an unescaped '.' before 'example.com', so it might match more hosts than expected. | tst-IncompleteHostnameRegExp.js:3:2:3:29 | /^http: ... le.com/ | here |
 | tst-IncompleteHostnameRegExp.js:6:3:6:28 | ^http:\\/\\/test.example.net | This regular expression has an unescaped '.' before 'example.net', so it might match more hosts than expected. | tst-IncompleteHostnameRegExp.js:6:2:6:29 | /^http: ... le.net/ | here |
 | tst-IncompleteHostnameRegExp.js:7:3:7:42 | ^http:\\/\\/test.(example-a\|example-b).com | This regular expression has an unescaped '.' before '(example-a\|example-b).com', so it might match more hosts than expected. | tst-IncompleteHostnameRegExp.js:7:2:7:43 | /^http: ... b).com/ | here |

javascript/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegExp/linkify-it/package.json

@@ -0,0 +1,6 @@
+{
+  "type": "module",
+  "dependencies": {
+    "linkify-it": "6.1.0"
+  }
+}

javascript/ql/test/query-tests/Security/CWE-020/IncompleteHostnameRegExp/linkify-it/tst-LinkifyIt.js

@@ -0,0 +1,21 @@
+import { LinkifyIt, linkifyit } from "linkify-it";
+import { LinkifyIt as OtherLinkifyIt } from "other-linkify-it";
+
+const scanner = new LinkifyIt({ fuzzyLink: false, fuzzyEmail: false })
+  .add("ftp:", null)
+  .add("mailto:", null)
+  .add("//", null);
+const text =
+  "😀 *literal* (https://www.youtube.com/watch?v=tax4e4hBBZc), then https://store.steampowered.com/app/457140/.";
+const matches = scanner.match(text);
+if (matches) {
+  console.log(matches.map((match) => match.raw));
+}
+
+if (new LinkifyIt().match("https://www.example.com")) {}
+if (new LinkifyIt().set({ fuzzyLink: false }).match("https://www.example.com")) {}
+if (new LinkifyIt().tlds("onion", true).match("https://www.example.com")) {}
+if (linkifyit().match("https://www.example.com")) {}
+
+const otherScanner = new OtherLinkifyIt().add("ftp:", null);
+if (otherScanner.match("^https://www.example.com")) {} // $ Alert

javascript/ql/test/query-tests/Security/CWE-020/MissingRegExpAnchor/tst-LinkifyIt.js

@@ -0,0 +1,7 @@
+const { LinkifyIt } = require("linkify-it");
+const legacyLinkifyIt = require("linkify-it");
+
+const scanner = new LinkifyIt().add("ftp:", null).set({ fuzzyLink: false });
+const text = "https://a.b.com";
+console.log(scanner.match(text));
+console.log(legacyLinkifyIt().match(text));

javascript/ql/test/query-tests/Security/CWE-730/Threat-models-disabled/RegExpInjectionGood.js

@@ -9,3 +9,12 @@ app.get('/findKey', function(req, res) {
   var safeKey = _.escapeRegExp(key);
   var re = new RegExp("\\b" + safeKey + "=(.*)\n");
 });
+
+var { LinkifyIt } = require("linkify-it");
+
+app.get('/findLinks', function(req, res) {
+  var text = req.param("text");
+  var scanner = new LinkifyIt().set({ fuzzyLink: false });
+  var matches = scanner.match(text);
+  res.json(matches);
+});