CVE-2016-7439 in wolfSSL
Summary
by MITRE
The C software implementation of RSA in wolfSSL (formerly CyaSSL) before 3.9.10 makes it easier for local users to discover RSA keys by leveraging cache-bank hit differences.
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Analysis
by VulDB Data Team • 06/25/2019
The vulnerability identified as CVE-2016-7439 affects the wolfSSL cryptographic library implementation of RSA algorithms, specifically targeting the software-based RSA implementation that was present in versions prior to 3.9.10. This issue represents a side-channel attack vector that exploits timing and cache behavior differences during cryptographic operations. The vulnerability is particularly concerning because it allows local attackers to potentially recover RSA private keys through sophisticated analysis of cache bank hit patterns, which is a form of cache-based side-channel attack that has been well-documented in cryptographic security research.
The technical flaw stems from the implementation of RSA exponentiation operations within the wolfSSL library where the software-based RSA calculations do not adequately mask the timing characteristics and cache access patterns that occur during modular exponentiation. When performing RSA operations, the cryptographic library accesses different memory locations and cache banks based on the bits of the private exponent, creating observable differences in cache hit rates that can be measured and analyzed. This vulnerability specifically targets the cache bank hit differences that occur during the RSA private key operations, making it possible for an attacker with local access to observe these patterns and reconstruct the private key through statistical analysis and machine learning techniques.
From an operational impact perspective, this vulnerability presents a significant risk to systems utilizing wolfSSL for secure communications, particularly in environments where local privilege escalation is possible or where attackers have access to the same system performing cryptographic operations. The attack requires local access to the system and the ability to monitor cache behavior, which makes it less likely to be exploited remotely but still poses a serious threat in compromised environments. The vulnerability affects any application that uses the affected version of wolfSSL for RSA key operations, potentially compromising the confidentiality and integrity of encrypted communications that rely on RSA-based authentication and encryption.
The mitigation strategy for CVE-2016-7439 involves upgrading to wolfSSL version 3.9.10 or later, which includes countermeasures against cache-based side-channel attacks. These countermeasures typically involve implementing constant-time algorithms for cryptographic operations, randomizing memory access patterns, and adding noise to timing measurements to prevent attackers from distinguishing between different cache access patterns. Organizations should also consider implementing additional security controls such as system hardening, access controls, and monitoring for unauthorized local access. The vulnerability aligns with CWE-310, which addresses cryptographic weaknesses, and may be related to ATT&CK techniques such as credential access through side-channel attacks and privilege escalation via local system compromise. System administrators should prioritize patching affected systems and conducting security assessments to ensure that no other vulnerable components exist in their cryptographic infrastructure.