CVE-2016-2178 in OpenSSL
Summary
by MITRE
The dsa_sign_setup function in crypto/dsa/dsa_ossl.c in OpenSSL through 1.0.2h does not properly ensure the use of constant-time operations, which makes it easier for local users to discover a DSA private key via a timing side-channel attack.
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Analysis
by VulDB Data Team • 08/29/2024
The vulnerability identified as CVE-2016-2178 resides within the OpenSSL cryptographic library version 1.0.2h and earlier, specifically within the dsa_sign_setup function located in the crypto/dsa/dsa_ossl.c file. This flaw represents a critical security weakness that undermines the fundamental principles of cryptographic implementation by failing to maintain constant-time operations during digital signature generation processes. The issue enables attackers to exploit timing side-channel vulnerabilities that can ultimately lead to the compromise of DSA private keys through careful analysis of execution time variations.
The technical root cause of this vulnerability stems from the improper implementation of constant-time algorithms within the DSA signature setup process. When generating digital signatures using the Digital Signature Algorithm, the cryptographic library should ensure that all operations take equivalent time regardless of the input values being processed. However, the dsa_sign_setup function fails to maintain this constant-time behavior, creating measurable differences in execution duration that correlate with the secret private key bits. This timing variation creates a leakage channel that can be exploited through sophisticated side-channel analysis techniques.
From an operational perspective, this vulnerability poses significant risks to systems relying on DSA-based digital signatures, particularly those using OpenSSL implementations. Local attackers with access to the target system can perform timing analysis attacks to gradually reconstruct the private key components. The attack typically involves measuring the time differences between various signature operations and correlating these measurements with the mathematical operations performed during key generation. This vulnerability affects the security of any application that depends on OpenSSL for DSA signature functionality, including but not limited to certificate authorities, secure communication protocols, and cryptographic applications that utilize DSA algorithms.
The impact of this vulnerability aligns with several established security frameworks and threat models. According to CWE classification, this represents a weakness in the implementation of cryptographic operations, specifically CWE-327 which deals with use of a broken or weak cryptographic algorithm. The vulnerability also maps to ATT&CK technique T1552.004 which involves exploitation of credential access through side-channel attacks. Organizations utilizing affected OpenSSL versions face potential compromise of their entire cryptographic infrastructure if they rely on DSA signatures for authentication, digital signatures, or key exchange mechanisms.
Mitigation strategies for CVE-2016-2178 require immediate action to upgrade to OpenSSL versions 1.0.2i or later, where the timing side-channel vulnerability has been addressed through proper constant-time implementation of cryptographic operations. System administrators should also consider implementing additional monitoring and detection mechanisms to identify potential exploitation attempts. The fix implemented in newer OpenSSL versions ensures that all mathematical operations within the signature generation process maintain consistent execution times regardless of input values, thereby eliminating the timing leakage that enabled the attack. Organizations should conduct comprehensive vulnerability assessments to identify all systems utilizing affected OpenSSL versions and ensure proper patching across their infrastructure.