CVE-2014-2903 in CyaSSL
Summary
by MITRE
CyaSSL does not check the key usage extension in leaf certificates, which allows remote attackers to spoof servers via a crafted server certificate not authorized for use in an SSL/TLS handshake.
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Analysis
by VulDB Data Team • 11/22/2019
The vulnerability identified as CVE-2014-2903 resides within the CyaSSL library, a lightweight SSL/TLS implementation designed for embedded systems and resource-constrained environments. This flaw represents a critical weakness in the certificate validation process that undermines the fundamental security guarantees of SSL/TLS communications. The issue specifically affects how the library handles certificate key usage extensions, which are critical components in the X.509 certificate framework that define the permitted cryptographic operations for a given certificate. When CyaSSL fails to validate these key usage extensions in leaf certificates, it creates a pathway for attackers to exploit the trust model by presenting certificates that should not be accepted for SSL/TLS server authentication.
The technical flaw manifests in the certificate validation routine where CyaSSL bypasses the verification of key usage extensions that are mandated by the X.509 standard and RFC 5280. Key usage extensions serve as critical access control mechanisms that specify which cryptographic operations a certificate may perform, such as digital signatures, key encipherment, or server authentication. In the context of SSL/TLS, certificates must include appropriate key usage extensions to indicate they are authorized for server authentication, typically requiring the digitalSignature and keyEncipherment key usage bits to be set. The absence of this validation in CyaSSL allows malicious actors to craft server certificates that contain unauthorized key usage combinations, yet the library still accepts these certificates as valid for TLS handshakes, effectively breaking the certificate chain validation process.
The operational impact of this vulnerability extends far beyond simple certificate validation failures, representing a significant threat to the integrity of secure communications. Remote attackers can exploit this weakness to perform man-in-the-middle attacks by presenting forged server certificates that appear valid to vulnerable CyaSSL implementations. This compromise enables attackers to intercept, modify, or redirect encrypted communications without detection, undermining the confidentiality and integrity assurances that SSL/TLS protocols are designed to provide. The vulnerability is particularly dangerous in embedded systems and IoT devices that rely on CyaSSL for secure communications, as these environments often lack robust security monitoring capabilities that might detect such attacks. The attack vector is straightforward and requires minimal sophistication, making it attractive to threat actors who can leverage this weakness to establish persistent surveillance or data exfiltration capabilities.
The vulnerability maps directly to CWE-310, which describes weaknesses in cryptographic key management, specifically focusing on the absence of proper validation of certificate key usage. From an ATT&CK framework perspective, this weakness enables techniques categorized under T1573.001 for "Encrypted Channels" and T1046 for "Network Service Scanning" as attackers can establish unauthorized secure connections. The lack of key usage validation creates a trust boundary violation that allows attackers to bypass the certificate validation process entirely, effectively neutralizing the security controls that should prevent unauthorized certificate usage. Organizations using CyaSSL in production environments must recognize that this vulnerability can be exploited across various protocols including HTTPS, SMTP, FTPS, and other TLS-enabled services where the library is deployed. The remediation requires immediate updates to the CyaSSL library to implement proper key usage extension validation, along with comprehensive security assessments of systems that rely on this cryptographic library.
Mitigation strategies should prioritize immediate library updates to versions that include proper certificate validation routines, while also implementing network-level monitoring to detect anomalous certificate behavior. Organizations should conduct thorough inventory assessments to identify all systems utilizing CyaSSL and ensure comprehensive patching across all affected devices. Additional defensive measures include implementing certificate pinning mechanisms where appropriate, deploying certificate transparency monitoring, and establishing network segmentation to limit the potential impact of successful exploitation. The vulnerability highlights the critical importance of proper certificate validation in cryptographic implementations and serves as a reminder that even lightweight libraries must maintain rigorous security standards to prevent fundamental trust model compromises that can undermine entire security architectures.