CVE-2016-7438 in wolfSSL
Summary
by MITRE
The C software implementation of ECC 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-2016-7438 affects the elliptic curve cryptography implementation within wolfSSL, a lightweight SSL/TLS library widely used in embedded systems and IoT devices. This issue resides in the software implementation of elliptic curve cryptography operations that are part of the broader cryptographic framework designed to provide secure communications. The vulnerability specifically impacts versions prior to 3.9.10, indicating that it represents a long-standing weakness in the cryptographic library that was not addressed until a significant update. The flaw manifests through a side-channel attack vector that exploits timing differences in cache memory access patterns during cryptographic operations.
The technical flaw exploited in this vulnerability stems from the implementation's susceptibility to cache timing attacks, where an attacker can observe and analyze the differences in cache bank hits during cryptographic computations. This particular weakness allows local adversaries to infer information about RSA private keys through careful measurement of cache access patterns. The attack leverages the fact that different memory access patterns during cryptographic operations result in measurable timing variations, which can be analyzed to reconstruct sensitive cryptographic information. The vulnerability represents a classic example of a timing side-channel attack that targets the underlying implementation rather than the cryptographic algorithm itself. This weakness is classified under CWE-310 as "Cryptographic Implementation Fault" and specifically relates to timing side-channel attacks that can leak information through cache behavior.
The operational impact of this vulnerability extends significantly beyond simple cryptographic weakness, as it enables local attackers to potentially compromise the security of systems relying on wolfSSL for secure communications. The vulnerability affects embedded systems, IoT devices, and other resource-constrained environments where wolfSSL is commonly deployed, making it particularly concerning for critical infrastructure and industrial control systems. An attacker with local access to a system running vulnerable wolfSSL versions could potentially recover RSA private keys through repeated cache timing measurements, leading to complete compromise of the cryptographic security. This vulnerability directly impacts the confidentiality and integrity of communications, as the exposure of RSA private keys would allow attackers to decrypt communications, forge signatures, and impersonate legitimate system components. The attack requires local access but can have far-reaching consequences for system security and trust relationships within networked environments.
Mitigation strategies for CVE-2016-7438 primarily involve upgrading to wolfSSL version 3.9.10 or later, which includes patches that address the cache timing side-channel vulnerability. Organizations should conduct comprehensive inventory assessments to identify all systems running vulnerable versions of wolfSSL and prioritize remediation efforts accordingly. Additional mitigations include implementing proper access controls to limit local user privileges, deploying intrusion detection systems to monitor for suspicious timing analysis activities, and considering the use of hardware security modules or dedicated cryptographic processors that provide better protection against cache timing attacks. Security teams should also consider implementing regular security assessments and vulnerability scanning to identify other potential side-channel vulnerabilities in their cryptographic implementations. The vulnerability underscores the importance of proper side-channel attack prevention in cryptographic software implementations and aligns with recommendations from the National Institute of Standards and Technology regarding cryptographic module validation and secure implementation practices.