CVE-2005-0366 in OpenPGP
Summary
by MITRE
The integrity check feature in OpenPGP, when handling a message that was encrypted using cipher feedback (CFB) mode, allows remote attackers to recover part of the plaintext via a chosen-ciphertext attack when the first 2 bytes of a message block are known, and an oracle or other mechanism is available to determine whether an integrity check failed.
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Analysis
by VulDB Data Team • 07/17/2024
The vulnerability described in CVE-2005-0366 resides within the OpenPGP implementation's integrity checking mechanism, specifically when processing messages encrypted using cipher feedback mode. This flaw represents a sophisticated cryptographic weakness that exploits the interaction between encryption modes and integrity verification protocols. The vulnerability manifests when an attacker can manipulate ciphertext and observe the system's response to integrity check failures, creating a side-channel attack vector that can reveal partial plaintext information.
The technical exploitation of this vulnerability relies on the chosen-ciphertext attack methodology, where an adversary can submit carefully crafted ciphertext to the system and observe whether integrity checks pass or fail. When messages are encrypted using cipher feedback mode, the encryption process operates on blocks where each block depends on the previous ciphertext block, creating a dependency chain that can be manipulated. The specific condition requiring the first 2 bytes of a message block to be known suggests that the attack exploits the predictable nature of these initial bytes, which often contain protocol-specific markers or headers.
This vulnerability directly relates to CWE-310, which addresses cryptographic weaknesses in integrity checking mechanisms, and can be categorized under the ATT&CK technique T1552.004 for unsecured cryptographic keys and T1071.004 for application layer protocols. The attack vector demonstrates how improper implementation of cryptographic integrity checks can create information leakage channels that bypass traditional encryption security models. The oracle mechanism that determines integrity check failures provides the attacker with a critical feedback loop that enables progressive plaintext recovery.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can potentially enable more sophisticated attacks such as full plaintext recovery or key compromise. When an attacker can repeatedly submit modified ciphertext and observe integrity check outcomes, they can iteratively reconstruct message content, particularly affecting sensitive communications where OpenPGP encryption is employed. The vulnerability affects systems that rely on OpenPGP for secure communication, potentially compromising the confidentiality of encrypted messages.
Mitigation strategies for this vulnerability require comprehensive cryptographic protocol updates and proper implementation of integrity checking mechanisms. Systems should implement authenticated encryption modes that combine encryption with integrity protection, such as GCM or CCM modes, rather than relying on separate encryption and integrity check components. The solution involves ensuring that integrity checks are performed in a way that does not provide side-channel information about check failures, typically through constant-time implementations or by using techniques that prevent attackers from distinguishing between different failure conditions. Additionally, implementing proper error handling that does not reveal whether an integrity check failed versus other types of errors helps prevent this class of attack. Organizations should also consider upgrading to modern cryptographic libraries that properly address these historical weaknesses in OpenPGP implementations, as the vulnerability stems from implementation flaws rather than fundamental cryptographic algorithm weaknesses.