The Azure Active Directory (AAD) authentication implementation contained multiple weaknesses in its OAuth 2.0 authorization flow that could allow attackers to bypass important security guarantees provided by the protocol.

The application used the PHP session identifier (session_id()) as the OAuth state parameter. Because session identifiers are long-lived authentication credentials, exposing them in OAuth redirect URLs could leak valid session tokens through browser history, HTTP Referer headers, reverse proxies, access logs, or third-party infrastructure involved in the authentication flow. If obtained by an attacker, the leaked session identifier could potentially be used for session hijacking.

Additionally, the implementation did not regenerate the session identifier after successful authentication, leaving authenticated sessions susceptible to session fixation attacks where an attacker forces a victim to use a known session identifier before login and later reuses that identifier after authentication.

The OAuth state value was also not implemented as a dedicated, single-use nonce. This weakened CSRF protections and increased the risk of replay attacks against the OAuth callback process.

The authentication flow further failed to enforce HTTPS for the configured OAuth redirect URI. If a non-HTTPS redirect URI was used, OAuth authorization codes and access tokens could traverse the network in plaintext, exposing sensitive credentials to network attackers.

Finally, OAuth error responses containing attacker-controlled GET parameters were logged verbatim. An attacker could inject control characters or crafted log content, leading to log forging, log injection, or corruption of audit records.

The fix introduces:

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A dedicated cryptographically random OAuth state value.

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Single-use state validation and invalidation.

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Constant-time state comparison using hash_equals().

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Session identifier rotation after successful authentication.

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Enforcement of HTTPS-only redirect URIs.

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Sanitized and length-limited logging of OAuth error parameters.

AAD Authentication Plugin (OAuth 2.0 / Azure Active Directory integration)