CVE-2015-0837 in Libgcrypt
Summary
by MITRE
The mpi_powm function in Libgcrypt before 1.6.3 and GnuPG before 1.4.19 allows attackers to obtain sensitive information by leveraging timing differences when accessing a pre-computed table during modular exponentiation, related to a "Last-Level Cache Side-Channel Attack."
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 12/02/2024
The vulnerability identified as CVE-2015-0837 represents a critical side-channel attack targeting cryptographic implementations within the Libgcrypt library and GnuPG software ecosystem. This flaw specifically affects versions prior to 1.6.3 of Libgcrypt and 1.4.19 of GnuPG, where the mpi_powm function demonstrates susceptibility to timing-based information leakage during modular exponentiation operations. The vulnerability exploits the Last-Level Cache (LLC) side-channel attack mechanism, which enables adversaries to infer sensitive cryptographic data through careful analysis of cache access patterns and timing variations.
The technical implementation of this vulnerability stems from the mpi_powm function's use of pre-computed tables during modular exponentiation calculations. When performing cryptographic operations, the function accesses these pre-computed tables in a manner that creates observable timing differences based on which cache lines are accessed. Attackers can exploit this timing variation by measuring the time taken for various cryptographic operations and correlating these measurements with cache hit/miss patterns. The vulnerability specifically targets the last-level cache, which represents the final level of cache hierarchy before memory access, making it particularly effective for information leakage attacks. This attack vector operates under the established framework of cache side-channel attacks, which are classified under CWE-310 in the Common Weakness Enumeration catalog.
The operational impact of CVE-2015-0837 extends significantly beyond simple information disclosure, as it can potentially compromise the security of cryptographic keys and sensitive data processed through affected software. When attackers successfully exploit this vulnerability, they can reconstruct private keys used in RSA and other public-key cryptographic algorithms, effectively undermining the fundamental security assumptions of these systems. The attack requires only passive observation of timing measurements and does not necessitate direct system compromise or privileged access, making it particularly dangerous in environments where cryptographic operations are performed on shared or multi-tenant systems. The vulnerability affects not just individual cryptographic operations but entire cryptographic protocols that rely on modular exponentiation, including SSL/TLS implementations, digital signatures, and key exchange mechanisms.
Mitigation strategies for this vulnerability primarily involve updating to patched versions of Libgcrypt and GnuPG where the timing variations have been eliminated through algorithmic improvements and cache-friendly implementation techniques. The recommended approach includes implementing constant-time algorithms that ensure consistent execution patterns regardless of input data, thereby preventing timing side-channel leakage. Security professionals should also consider deploying cache clearing mechanisms and implementing additional monitoring for unusual timing variations in cryptographic operations. Organizations should conduct comprehensive vulnerability assessments to identify systems running affected versions and prioritize patch deployment. The ATT&CK framework categorizes this vulnerability under the technique of "Cache Side-Channel Attack" and "Timing Side-Channel Attack" within the broader category of credential access and defense evasion, highlighting the need for both preventive measures and detection capabilities. Additionally, implementing proper cryptographic library configuration and ensuring regular security updates form essential components of a comprehensive mitigation strategy against this specific class of side-channel vulnerabilities.