Security update for signature validation on LogoutRequest/LogoutResponse.

In order to verify Signatures on Logoutrequests and LogoutResponses we use
the verifySignature of the class XMLSecurityKey from the xmlseclibs library.
That method end up calling openssl_verify() depending on the signature algorithm used.

The openssl_verify() function returns 1 when the signature was successfully verified,
0 if it failed to verify with the given key, and -1 in case an error occurs.
PHP allows translating numerical values to boolean implicitly, with the following correspondences:
- 0 equals false.
- Non-zero equals true.

This means that an implicit conversion to boolean of the values returned by openssl_verify()
will convert an error state, signaled by the value -1, to a successful verification of the
signature (represented by the boolean true).

The LogoutRequest/LogoutResponse signature validator was performing an implicit conversion to boolean
of the values returned by the verify() method, which subsequently will return the same output
as openssl_verify() under most circumstances.
This means an error during signature verification is treated as a successful verification by the method.

Since the signature validation of SAMLResponses were not affected, the impact of this security
vulnerability is lower, but an update of the php-saml toolkit is recommended.

Author: pitbulk

lib/Saml2/LogoutRequest.php

@@ -402,7 +402,7 @@ public function isValid($retrieveParametersFromServer=false)
                     }
                 }
 
-                if (!$objKey->verifySignature($signedQuery, base64_decode($_GET['Signature']))) {
+                if ($objKey->verifySignature($signedQuery, base64_decode($_GET['Signature'])) !== 1) {
                     throw new OneLogin_Saml2_ValidationError(
                         "Signature validation failed. Logout Request rejected",
                         OneLogin_Saml2_ValidationError::INVALID_SIGNATURE

lib/Saml2/LogoutResponse.php

@@ -209,7 +209,7 @@ public function isValid($requestId = null, $retrieveParametersFromServer=false)
                     }
                 }
 
-                if (!$objKey->verifySignature($signedQuery, base64_decode($_GET['Signature']))) {
+                if ($objKey->verifySignature($signedQuery, base64_decode($_GET['Signature'])) !== 1) {
                     throw new OneLogin_Saml2_ValidationError(
                         "Signature validation failed. Logout Response rejected",
                         OneLogin_Saml2_ValidationError::INVALID_SIGNATURE