Publish GHSA-4v6x-c7xx-hw9f

Author: advisory-database[bot]

advisories/github-reviewed/2026/03/GHSA-4v6x-c7xx-hw9f/GHSA-4v6x-c7xx-hw9f.json

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+{
+  "schema_version": "1.4.0",
+  "id": "GHSA-4v6x-c7xx-hw9f",
+  "modified": "2026-03-06T23:27:03Z",
+  "published": "2026-03-06T23:27:03Z",
+  "aliases": [
+    "CVE-2026-30838"
+  ],
+  "summary": "CommonMark has DisallowedRawHtml extension bypass via whitespace in HTML tag names",
+  "details": "### Impact\n\nThe `DisallowedRawHtml` extension can be bypassed by inserting a newline, tab, or other ASCII whitespace character between a disallowed HTML tag name and the closing `>`. For example, `<script\\n>` would pass through unfiltered and be rendered as a valid HTML tag by browsers. This is a cross-site scripting (XSS) vector for any application that relies on this extension to sanitize untrusted user input.\n\nAll applications using the `DisallowedRawHtml` extension to process untrusted markdown are affected. Applications that use a dedicated HTML sanitizer (such as HTML Purifier) on the rendered output are not affected.\n\n### Patches\n\nFixed in 2.8.1. The regex character class `[ \\/>]` was changed to `[\\s\\/>]` to match all whitespace characters that browsers accept as valid tag name terminators.\n\n### Workarounds\n\n- Set the `html_input` configuration option to `'escape'` or `'strip'` to disable all raw HTML, though this is a broader restriction than the `DisallowedRawHtml` extension provides.\n- Pass the rendered HTML through a dedicated HTML sanitizer before serving it to users ([always recommended](https://commonmark.thephpleague.com/2.x/security/#additional-filtering))\n\n### Resources\n\n- [CommonMark DisallowedRawHtml documentation](https://commonmark.thephpleague.com/extensions/disallowed-raw-html/)\n- [CWE-79: Improper Neutralization of Input During Web Page Generation](https://cwe.mitre.org/data/definitions/79.html)\n- [CWE-80: Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)](https://cwe.mitre.org/data/definitions/80.html)",
+  "severity": [
+    {
+      "type": "CVSS_V4",
+      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N"
+    }
+  ],
+  "affected": [
+    {
+      "package": {
+        "ecosystem": "Packagist",
+        "name": "league/commonmark"
+      },
+      "ranges": [
+        {
+          "type": "ECOSYSTEM",
+          "events": [
+            {
+              "introduced": "0"
+            },
+            {
+              "fixed": "2.8.1"
+            }
+          ]
+        }
+      ],
+      "database_specific": {
+        "last_known_affected_version_range": "<= 2.8.0"
+      }
+    }
+  ],
+  "references": [
+    {
+      "type": "WEB",
+      "url": "https://github.com/thephpleague/commonmark/security/advisories/GHSA-4v6x-c7xx-hw9f"
+    },
+    {
+      "type": "WEB",
+      "url": "https://commonmark.thephpleague.com/extensions/disallowed-raw-html"
+    },
+    {
+      "type": "PACKAGE",
+      "url": "https://github.com/thephpleague/commonmark"
+    }
+  ],
+  "database_specific": {
+    "cwe_ids": [
+      "CWE-79"
+    ],
+    "severity": "MODERATE",
+    "github_reviewed": true,
+    "github_reviewed_at": "2026-03-06T23:27:03Z",
+    "nvd_published_at": null
+  }
+}