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Moderate severityNVD Advisory· Published Dec 1, 2025· Updated Dec 2, 2025

mdast-util-to-hast unsanitized class attribute

CVE-2025-66400

Description

mdast-util-to-hast is an mdast utility to transform to hast. From 13.0.0 to before 13.2.1, multiple (unprefixed) classnames could be added in markdown source by using character references. This could make rendered user supplied markdown code elements appear like the rest of the page. This vulnerability is fixed in 13.2.1.

Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
mdast-util-to-hastnpm
>= 13.0.0, < 13.2.113.2.1

Affected products

1

Patches

2
ab3a79570a1a

Fix support for spaces in class names

https://github.com/syntax-tree/mdast-util-to-hastTitus WormerNov 23, 2025via ghsa
commit
2 files changed · +12 −2
  • lib/handlers/code.js+5 −2 modified
    @@ -18,9 +18,12 @@ export function code(state, node) {
   const value = node.value ? node.value + '\n' : ''
   /** @type {Properties} */
   const properties = {}
+  // Someone can write `js&#x20;python&#x9;ruby`.
+  const language = node.lang ? node.lang.split(/\s+/) : []
 
-  if (node.lang) {
-    properties.className = ['language-' + node.lang]
+  // GH/CM still drop the non-first languages.
+  if (language.length > 0) {
+    properties.className = ['language-' + language[0]]
   }
 
   // Create `<code>`.
  • test/code.js+7 −0 modified
    @@ -34,6 +34,13 @@ test('code', async function (t) {
     }
   )
 
+  await t.test('should transform `lang` w/ spaces', async function () {
+    assert.deepEqual(
+      toHast({type: 'code', lang: 'js python\truby', value: 'echo()'}),
+      h('pre', [h('code', {className: ['language-js']}, 'echo()\n')])
+    )
+  })
+
   await t.test('should support `meta`', async function () {
     assert.deepEqual(
       toHast({type: 'code', lang: 'js', meta: 'echo', value: 'foxtrot()'}),
6fc783ae6abd

Change to remove support for ancient `lang` on `code` with spaces

https://github.com/syntax-tree/mdast-util-to-hastTitus WormerJul 16, 2023via ghsa
commit
1 file changed · +2 −5
  • lib/handlers/code.js+2 −5 modified
    @@ -20,14 +20,11 @@
  */
 export function code(state, node) {
   const value = node.value ? node.value + '\n' : ''
-  // To do: next major, use `node.lang` w/o regex, the splitting’s been going
-  // on for years in remark now.
-  const lang = node.lang ? node.lang.match(/^[^ \t]+(?=[ \t]|$)/) : undefined
   /** @type {Properties} */
   const properties = {}
 
-  if (lang) {
-    properties.className = ['language-' + lang]
+  if (node.lang) {
+    properties.className = ['language-' + node.lang]
   }
 
   // Create `<code>`.

Vulnerability mechanics

Generated by null/stub on May 9, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.

References

5

News mentions

0

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