CVE-2016-0736 in macOS
Summary
by MITRE
In Apache HTTP Server versions 2.4.0 to 2.4.23, mod_session_crypto was encrypting its data/cookie using the configured ciphers with possibly either CBC or ECB modes of operation (AES256-CBC by default), hence no selectable or builtin authenticated encryption. This made it vulnerable to padding oracle attacks, particularly with CBC.
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Analysis
by VulDB Data Team • 01/20/2025
The vulnerability described in CVE-2016-0736 affects Apache HTTP Server versions 2.4.0 through 2.4.23 and specifically targets the mod_session_crypto module. This module was designed to provide session management capabilities by encrypting session data stored in cookies, creating a mechanism for maintaining user sessions across HTTP requests without requiring server-side storage. The flaw lies in how the encryption was implemented within this module, particularly when utilizing the Advanced Encryption Standard with AES256-CBC as the default cipher mode. The vulnerability stems from the use of cipher block chaining mode of operation which, while providing confidentiality, lacks authentication mechanisms that would prevent attackers from manipulating encrypted data without detection.
The technical implementation of mod_session_crypto in affected Apache versions employed encryption algorithms without proper authenticated encryption, leaving the system susceptible to padding oracle attacks. When CBC mode encryption is used without authentication, attackers can exploit the predictable nature of padding validation responses to gradually decrypt session data through a series of carefully crafted requests. This attack vector specifically targets the padding validation mechanism inherent to CBC mode, where incorrect padding in decrypted blocks generates distinct error responses that can be used to infer information about the plaintext. The vulnerability is particularly severe because it allows attackers to potentially recover session tokens and user credentials stored in encrypted cookies, effectively bypassing session management security controls that should have protected user sessions.
The operational impact of this vulnerability extends beyond simple session hijacking, as it provides attackers with the capability to modify session data in transit without detection, potentially leading to privilege escalation or unauthorized access to protected resources. Attackers could leverage this weakness to impersonate legitimate users, access restricted content, or perform actions within applications that rely on Apache's session management for authentication. The vulnerability affects organizations running Apache HTTP Server in environments where session-based authentication is implemented, particularly web applications that store sensitive information in encrypted cookies. The attack requires relatively minimal sophistication and can be automated, making it a significant threat to web application security. According to CWE classification, this vulnerability maps to CWE-310, which addresses cryptographic weaknesses, specifically focusing on the use of insecure encryption modes without proper authentication.
Organizations affected by this vulnerability should immediately implement mitigations including upgrading to Apache HTTP Server version 2.4.24 or later, where the mod_session_crypto module was properly updated to use authenticated encryption modes. Alternative approaches include disabling the mod_session_crypto module if session data is not critical, or implementing additional security controls such as secure cookie attributes and session management best practices. The mitigation strategy should also include monitoring for suspicious session-related activity and implementing proper cryptographic key management practices. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving credential access and privilege escalation, specifically targeting the credential stuffing and session management weaknesses that attackers exploit to maintain persistent access to systems. Organizations should also consider implementing web application firewalls and intrusion detection systems to help detect and prevent exploitation attempts targeting this specific vulnerability.