CVE-2021-41393 in Teleport
Summary
by MITRE • 09/18/2021
Teleport before 4.4.11, 5.x before 5.2.4, 6.x before 6.2.12, and 7.x before 7.1.1 allows forgery of SSH host certificates in some situations.
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Analysis
by VulDB Data Team • 09/22/2021
The vulnerability identified as CVE-2021-41393 represents a critical security flaw in the Teleport remote access platform that affects multiple version ranges including 4.4.11 and earlier, 5.x versions before 5.2.4, 6.x versions before 6.2.12, and 7.x versions before 7.1.1. This issue specifically targets the SSH host certificate validation mechanism within the Teleport system, creating a potential avenue for attackers to forge legitimate SSH certificates and gain unauthorized access to systems protected by Teleport. The flaw resides in the certificate validation process where proper signature verification and certificate chain validation are not consistently enforced, allowing malicious actors to craft and present forged certificates that appear legitimate to the Teleport system.
The technical implementation of this vulnerability stems from inadequate certificate validation logic within Teleport's SSH certificate handling components. When Teleport processes SSH host certificates, it fails to properly validate the certificate signature chain or verify that certificates are issued by trusted Certificate Authority entities. This weakness allows attackers to exploit the system's trust model by creating forged certificates that bypass the normal certificate validation procedures. The vulnerability manifests particularly in scenarios where Teleport is configured to trust certificates from unverified sources or when certificate authority validation is disabled or improperly configured. This flaw aligns with CWE-347, which addresses improper certificate validation, and represents a significant weakness in the system's authentication and authorization framework.
The operational impact of CVE-2021-41393 extends beyond simple unauthorized access to potentially enabling sophisticated attack vectors that can compromise entire network infrastructures. An attacker exploiting this vulnerability could establish persistent access to systems, bypass multi-factor authentication mechanisms, and move laterally within networks where Teleport is deployed. The forged certificates could be used to impersonate legitimate SSH hosts, allowing attackers to gain access to sensitive systems without proper authentication. This vulnerability directly impacts the principle of least privilege and can enable privilege escalation scenarios where attackers can access systems they should not have authorization to reach. Organizations using Teleport for remote access management face significant risk of data breaches, insider threat exploitation, and compliance violations due to this certificate forgery capability. The attack pattern described in the ATT&CK framework under T1550.003 for 'Use Alternate Authentication Material' is particularly relevant as this vulnerability enables attackers to leverage forged certificates as a means of authentication bypass.
Mitigation strategies for CVE-2021-41393 require immediate patching of affected Teleport versions to the recommended secure releases that address the certificate validation flaws. Organizations should implement strict certificate authority validation policies and ensure that all SSH host certificates are properly signed by trusted entities with valid certificate chains. Network segmentation and monitoring should be enhanced to detect unusual certificate validation patterns or unauthorized certificate usage. Security teams should also consider implementing certificate pinning mechanisms and regular certificate inventory audits to identify potentially compromised certificates. The remediation process should include thorough testing of patched systems to ensure that certificate validation works correctly and that no regression issues have been introduced. Additionally, organizations should review their Teleport configuration files to ensure that certificate validation parameters are properly enforced and that default configurations that might disable validation are addressed. Regular security assessments and penetration testing should be conducted to verify that the certificate validation mechanisms are functioning as expected and that no other related vulnerabilities exist within the Teleport deployment.