CVE-2017-7526 in Libgcrypt
Summary
by MITRE
libgcrypt before version 1.7.8 is vulnerable to a cache side-channel attack resulting into a complete break of RSA-1024 while using the left-to-right method for computing the sliding-window expansion. The same attack is believed to work on RSA-2048 with moderately more computation. This side-channel requires that attacker can run arbitrary software on the hardware where the private RSA key is used.
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Analysis
by VulDB Data Team • 12/14/2022
The vulnerability identified as CVE-2017-7526 represents a critical cache side-channel attack against the libgcrypt cryptographic library, specifically targeting RSA key operations. This weakness affects versions prior to 1.7.8 and demonstrates how modern microarchitectural features can be exploited to compromise cryptographic security. The attack exploits the timing variations in cache memory access patterns during RSA computations, particularly when using the left-to-right method for sliding-window expansion. This represents a sophisticated form of side-channel analysis that leverages the fundamental architecture of modern processors rather than traditional software vulnerabilities.
The technical flaw manifests in the way libgcrypt handles RSA private key operations through the sliding-window algorithm with left-to-right computation. During these operations, the cryptographic library accesses memory locations in patterns that correlate with the secret key bits being processed. When an attacker can execute code on the same hardware where the RSA private key operations occur, they can monitor cache access patterns to infer information about the secret key. This vulnerability is particularly severe because it targets the core mathematical operations that underpin RSA encryption security. The attack can completely break RSA-1024 keys, which is a significant concern given the widespread use of this key size in various cryptographic applications. The underlying mechanism aligns with CWE-310, which addresses cryptographic weaknesses related to side-channel attacks and information leakage through implementation details.
The operational impact of this vulnerability extends beyond simple key recovery, as it fundamentally undermines the security assumptions of RSA-based systems that rely on the secrecy of private keys. Attackers with code execution privileges on systems performing RSA operations can reconstruct private keys through statistical analysis of cache access patterns, effectively neutralizing the security guarantees provided by RSA encryption. This vulnerability is particularly dangerous in environments where multiple users share the same hardware or when the cryptographic operations occur on systems that might be compromised. The attack requires the attacker to have the ability to run arbitrary code on the target system, which represents a significant privilege level but is achievable in various threat scenarios including compromised web servers, cloud environments, or systems with insufficient isolation mechanisms. The vulnerability demonstrates the critical importance of considering microarchitectural side channels in cryptographic implementations and aligns with ATT&CK technique T1059 which covers execution of malicious code.
Mitigation strategies for this vulnerability require immediate upgrading to libgcrypt version 1.7.8 or later, which includes patches that address the cache side-channel exposure. Organizations should also implement additional security measures such as ensuring proper system isolation, monitoring for unauthorized code execution, and considering the use of constant-time implementations where possible. System administrators should conduct thorough inventory checks to identify all systems using vulnerable libgcrypt versions and implement remediation procedures. The vulnerability highlights the necessity of comprehensive security testing that includes side-channel analysis, particularly for cryptographic libraries that handle sensitive operations. Regular security updates and patch management procedures become critical in preventing exploitation of such architecture-level vulnerabilities that can bypass traditional software security controls.