CVE-2026-26022: Gogs Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-xrcr-gmf5-2r8j",
  "modified" : "2026-03-05T22:28:35Z",
  "published" : "2026-03-05T19:26:02Z",
  "aliases" : [ "CVE-2026-26022" ],
  "summary" : "Gogs: Stored XSS via data URI in issue comments",
  "details" : "### Summary\nA Stored Cross-site Scripting (XSS) vulnerability exists in the comment and issue description functionality. The application's HTML sanitizer explicitly allows `data:` URI schemes, enabling authenticated users to inject arbitrary JavaScript execution via malicious links.\n\n### Details\nThe vulnerability is located in `internal/markup/sanitizer.go`. The application uses the `bluemonday` HTML sanitizer but explicitly weakens the security policy by allowing the `data` URL scheme:\n\n```go\n// internal/markup/sanitizer.go\nfunc NewSanitizer() {\n    sanitizer.init.Do(func() {\n        // ...\n        // Data URLs\n        sanitizer.policy.AllowURLSchemes(\"data\")\n        // ...\n    })\n}\n```\n\nWhile the Markdown renderer rewrites relative links (mitigating standard Markdown `[link](data:...)` attacks), Gogs supports **Raw HTML** input. Raw HTML anchor tags bypass the Markdown parser's link rewriting and are processed directly by the sanitizer. Since the sanitizer is configured to allow `data:` URIs, payloads like `<a href=\"data:text/html...\">` are rendered as-is.\n\n### PoC\n1.  Create a file named `exploit.md` in a repository.\n2.  Add the following content (Raw HTML):\n    ```html\n    <a href=\"data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4=\">Click me for XSS</a>\n    ```\n3.  Commit and push the file.\n4.  Navigate to the file in the Gogs web interface.\n5.  Click the \"Click me for XSS\" link.\n6.  **Result:** An alert box with \"XSS\" appears, executing the JavaScript payload.\n\n### Impact\nThis is a **Stored XSS** vulnerability. Any user who views the malicious comment and clicks the link will execute the attacker-supplied JavaScript in their browser context. This allows attackers to:\n*   Steal authentication cookies and session tokens.\n*   Perform arbitrary actions on behalf of the victim (e.g., modifying repositories, adding collaborators).\n*   Redirect users to malicious sites.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "gogs.io/gogs"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.14.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.14.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/gogs/gogs/security/advisories/GHSA-xrcr-gmf5-2r8j"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-26022"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/gogs/gogs/pull/8174"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/gogs/gogs/commit/441c64d7bd8893b2f4e48660a8be3a7472e14291"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/gogs/gogs"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/gogs/gogs/releases/tag/v0.14.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-05T19:26:02Z",
    "nvd_published_at" : "2026-03-05T19:16:03Z"
  }
}