CVE-2017-14032 in ARM mbed TLS
Summary
by MITRE
ARM mbed TLS before 1.3.21 and 2.x before 2.1.9, if optional authentication is configured, allows remote attackers to bypass peer authentication via an X.509 certificate chain with many intermediates. NOTE: although mbed TLS was formerly known as PolarSSL, the releases shipped with the PolarSSL name are not affected.
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Analysis
by VulDB Data Team • 06/05/2026
The vulnerability identified as CVE-2017-14032 affects ARM mbed TLS versions prior to 1.3.21 and 2.x prior to 2.1.9, specifically when optional authentication is configured within the X.509 certificate chain validation process. This flaw represents a significant security weakness in the cryptographic library's certificate validation mechanism that could be exploited by remote attackers to bypass critical peer authentication requirements. The vulnerability stems from improper handling of X.509 certificate chains containing numerous intermediate certificates, creating a potential attack vector that undermines the integrity of secure communications.
The technical root cause of this vulnerability lies in the certificate chain validation logic within mbed TLS, where the library fails to properly enforce authentication constraints when processing X.509 certificate chains with excessive intermediate certificates. This issue manifests when the certificate validation process does not adequately verify the complete chain of trust, allowing attackers to construct certificate chains with many intermediates that bypass the expected authentication checks. The flaw specifically impacts configurations where optional authentication is enabled, creating a scenario where the validation process becomes vulnerable to manipulation through certificate chain construction. This weakness aligns with CWE-295, which addresses improper certificate validation, and represents a failure in certificate chain validation that could be exploited through certificate manipulation techniques.
The operational impact of CVE-2017-14032 extends beyond simple authentication bypass to potentially compromise the entire security infrastructure that relies on mbed TLS for secure communications. Remote attackers can exploit this vulnerability to establish fraudulent secure connections, impersonate legitimate services, or conduct man-in-the-middle attacks against systems using affected mbed TLS versions. The vulnerability affects systems implementing TLS/SSL protocols where certificate authentication is configured as optional, making it particularly dangerous for applications that depend on certificate-based authentication for security. This flaw can undermine the trust model of secure communications, potentially allowing unauthorized access to sensitive data and systems. The impact is further amplified because the vulnerability can be exploited without requiring local access or elevated privileges, making it a significant concern for network security.
Mitigation strategies for CVE-2017-14032 primarily involve upgrading to patched versions of mbed TLS, specifically versions 1.3.21 or later for the 1.x series and 2.1.9 or later for the 2.x series. Organizations should conduct comprehensive inventory assessments to identify all systems using vulnerable mbed TLS versions and prioritize patching activities accordingly. Additionally, security teams should review their certificate validation configurations to ensure that optional authentication is properly implemented and that certificate chain validation enforces appropriate constraints. The ATT&CK framework categorizes this vulnerability under credential access techniques, specifically related to certificate manipulation and authentication bypass methods. System administrators should also consider implementing additional monitoring and logging mechanisms to detect potential exploitation attempts, as the vulnerability may be used in conjunction with other attack vectors. Regular security assessments and vulnerability scanning should be performed to ensure that all components using mbed TLS remain up to date with the latest security patches.