CVE-2016-6474 in IOS
Summary
by MITRE
A vulnerability in the implementation of X.509 Version 3 for SSH authentication functionality in Cisco IOS and IOS XE Software could allow an unauthenticated, remote attacker to bypass authentication on an affected system. More Information: CSCuv89417. Known Affected Releases: 15.5(2.25)T. Known Fixed Releases: 15.2(4)E1 15.2(4)E2 15.2(4)E3 15.2(4)EA4 15.2(4.0r)EB 15.2(4.1.27)EB 15.2(4.4.2)EA4 15.2(4.7.1)EC 15.2(4.7.2)EC 15.2(5.1.1)E 15.2(5.5.63)E 15.2(5.5.64)E 15.4(1)IA1.80 15.5(3)M1.1 15.5(3)M2 15.5(3)S1.4 15.5(3)S2 15.6(0.22)S0.12 15.6(1)T0.1 15.6(1)T1 15.6(1.15)T 15.6(1.17)S0.7 15.6(1.17)SP 15.6(1.22.1a)T0 15.6(2)S 15.6(2)SP 16.1(1.24) 16.1.2 16.2(0.247) 16.3(0.11) 3.8(1)E Denali-16.1.2.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-6474 represents a critical authentication bypass flaw within Cisco IOS and IOS XE Software implementations of X.509 Version 3 SSH authentication mechanisms. This weakness stems from improper handling of X.509 certificates during the Secure Shell authentication process, creating a pathway for unauthenticated remote attackers to gain system access without proper credentials. The vulnerability specifically affects the certificate validation logic that should enforce strict authentication requirements but instead allows malicious actors to circumvent these security controls through crafted certificate parameters.
This authentication bypass vulnerability operates at the core of the Secure Shell protocol implementation within Cisco networking devices, where X.509 certificates are expected to validate user identities and establish secure connections. The flaw manifests when the system processes X.509 Version 3 certificates during SSH authentication, allowing attackers to exploit weaknesses in the certificate validation routine that should normally reject improperly formatted or unauthorized certificates. The vulnerability's impact extends across multiple software versions and device types, making it particularly concerning for network administrators managing diverse Cisco infrastructure deployments. According to the Cisco Security Advisory CSCuv89417, this issue affects systems running specific IOS and IOS XE releases, with the vulnerability being present in versions that implement the problematic X.509 certificate handling logic.
The operational impact of CVE-2016-6474 is severe and far-reaching, as it enables remote attackers to gain unauthorized access to network devices without requiring legitimate credentials or authentication. This vulnerability directly violates fundamental security principles of access control and authentication, potentially allowing attackers to execute arbitrary commands, modify network configurations, or establish persistent backdoors within the affected systems. The remote nature of the attack means that adversaries can exploit this flaw from outside the network perimeter, making traditional network segmentation and perimeter defenses ineffective against this specific threat vector. Organizations may face complete compromise of their network infrastructure if this vulnerability remains unpatched, as attackers could potentially gain administrative access to routers, switches, and other networking equipment that form the backbone of their network operations.
Mitigation strategies for CVE-2016-6474 primarily focus on implementing the vendor-provided security patches and updates that address the specific X.509 certificate validation flaw. Network administrators should prioritize upgrading affected systems to the fixed releases identified in the vulnerability advisory, which include various IOS and IOS XE versions from multiple release streams. Additionally, organizations should implement network segmentation measures to limit the potential impact of exploitation, disable unnecessary SSH services where possible, and monitor network traffic for suspicious authentication attempts. The mitigation approach aligns with the principle of least privilege and defense in depth, as recommended by cybersecurity frameworks such as the NIST Cybersecurity Framework and ISO 27001 standards. Security teams should also consider implementing additional monitoring controls to detect anomalous authentication patterns that might indicate exploitation attempts, particularly focusing on X.509 certificate related events within SSH sessions. This vulnerability demonstrates the critical importance of proper certificate handling in authentication systems and highlights the need for comprehensive security testing of cryptographic implementations, which aligns with CWE categories related to improper certificate validation and authentication bypass mechanisms.