CVE-2018-0733 in OpenSSL
Summary
by MITRE
Because of an implementation bug the PA-RISC CRYPTO_memcmp function is effectively reduced to only comparing the least significant bit of each byte. This allows an attacker to forge messages that would be considered as authenticated in an amount of tries lower than that guaranteed by the security claims of the scheme. The module can only be compiled by the HP-UX assembler, so that only HP-UX PA-RISC targets are affected. Fixed in OpenSSL 1.1.0h (Affected 1.1.0-1.1.0g).
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Analysis
by VulDB Data Team • 02/24/2023
The vulnerability identified as CVE-2018-0733 represents a critical cryptographic weakness in the OpenSSL implementation specifically affecting HP-UX PA-RISC systems. This flaw manifests in the PA-RISC CRYPTO_memcmp function which is designed to perform constant-time memory comparison operations essential for cryptographic security. The implementation bug fundamentally compromises the integrity of authentication mechanisms by reducing the effective comparison to only the least significant bit of each byte, creating a severe weakness in the cryptographic verification process. This vulnerability falls under the CWE-295 category of Improper Certificate Validation, as it directly impacts the trust verification mechanisms that cryptographic systems rely upon for secure communications.
The technical flaw occurs within the PA-RISC assembly implementation of the CRYPTO_memcmp function where the comparison logic is incorrectly implemented to only examine the least significant bit of each byte during memory comparison operations. This represents a fundamental violation of constant-time comparison principles that cryptographic implementations must follow to prevent timing attacks and ensure that all possible bit combinations are equally likely to be examined during verification processes. The vulnerability creates a scenario where an attacker can exploit the reduced security margin to forge authenticated messages, significantly decreasing the computational effort required to bypass authentication mechanisms compared to the theoretical security guarantees provided by the cryptographic scheme.
The operational impact of this vulnerability is particularly severe for systems running OpenSSL 1.1.0 through 1.1.0g on HP-UX PA-RISC platforms, as it directly undermines the security of all cryptographic protocols that depend on the CRYPTO_memcmp function for authentication verification. This includes but is not limited to TLS/SSL connections, digital signatures, and other security protocols that rely on secure memory comparison operations to validate authenticity. The reduced effective security margin means that attackers can successfully forge messages with a dramatically lower computational cost than the security model would suggest, potentially leading to unauthorized access, data tampering, and complete compromise of secure communication channels. This vulnerability directly maps to ATT&CK technique T1552.001 for Unsecured Credentials and T1071.004 for Application Layer Protocol: DNS, as it undermines the cryptographic foundations that protect these communication channels.
The fix implemented in OpenSSL 1.1.0h addresses this vulnerability by correcting the PA-RISC assembly implementation to properly perform full byte comparisons across all bits rather than limiting the comparison to only the least significant bit. This remediation ensures that cryptographic verification operations maintain their intended security properties and that the constant-time characteristics of memory comparison functions are preserved. Organizations using HP-UX PA-RISC systems should immediately upgrade to OpenSSL 1.1.0h or later versions to eliminate this vulnerability. System administrators should also verify that the specific PA-RISC assembly code has been properly compiled and deployed, as the vulnerability is specifically tied to the HP-UX assembler implementation and does not affect other platforms or architectures. The remediation addresses the core issue identified in CWE-310 and aligns with security best practices for cryptographic implementation as outlined in NIST SP 800-131A and other cryptographic standards.