CVE-2017-7562 in krb5 certauth Interface
Summary
by MITRE
An authentication bypass flaw was found in the way krb5's certauth interface before 1.16.1 handled the validation of client certificates. A remote attacker able to communicate with the KDC could potentially use this flaw to impersonate arbitrary principals under rare and erroneous circumstances.
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Analysis
by VulDB Data Team • 04/25/2023
The vulnerability identified as CVE-2017-7562 represents a critical authentication bypass flaw within the Kerberos 5 (krb5) implementation's certauth interface. This issue affects versions prior to 1.16.1 and fundamentally compromises the integrity of the authentication process by allowing unauthorized entities to potentially impersonate legitimate principals. The flaw resides in the certificate validation mechanism that governs how the Key Distribution Center processes client certificates, creating a pathway for malicious actors to circumvent normal authentication procedures. The vulnerability's impact is particularly concerning because it operates at the core of Kerberos authentication infrastructure, which serves as the foundation for secure network authentication in numerous enterprise environments and operating systems.
The technical root cause of this vulnerability stems from improper validation of client certificates within the certauth interface of krb5's KDC implementation. Specifically, the flaw occurs when the system fails to properly verify certificate attributes and validation parameters during the authentication process. This insufficient validation allows attackers to craft specially formatted certificate requests that bypass normal certificate checking procedures, enabling them to present forged credentials that the system accepts as legitimate. The vulnerability manifests under specific and rare circumstances, making it particularly insidious as it may go undetected during routine security monitoring. The flaw essentially creates a condition where the certificate validation logic becomes ineffective, allowing malformed or unauthorized certificates to be accepted without proper scrutiny.
The operational impact of CVE-2017-7562 extends far beyond simple authentication bypass, as it fundamentally undermines the trust model that Kerberos relies upon for secure network communications. In practical terms, this vulnerability could enable attackers to gain unauthorized access to sensitive systems, escalate privileges within authenticated environments, and potentially move laterally across networks where Kerberos authentication is employed. The rarity of the circumstances under which this vulnerability operates makes it particularly dangerous because administrators may not anticipate such a flaw in a core authentication component. Organizations using krb5 implementations in critical infrastructure, enterprise networks, or systems requiring strong authentication guarantees face significant risk from this vulnerability, as it could allow attackers to impersonate any principal within the Kerberos realm without proper authorization.
Mitigation strategies for CVE-2017-7562 primarily involve upgrading to krb5 version 1.16.1 or later, which includes patches addressing the certificate validation flaw. Organizations should also implement additional monitoring and logging of authentication events to detect anomalous certificate usage patterns that might indicate exploitation attempts. Security teams should conduct thorough assessments of their Kerberos implementations to identify systems running vulnerable versions and ensure proper certificate management practices are in place. The vulnerability aligns with CWE-287, which addresses improper authentication issues, and represents a significant concern from an ATT&CK perspective under the privilege escalation and defense evasion tactics. Organizations should also consider implementing certificate transparency measures and regular certificate audits as additional safeguards against similar vulnerabilities in authentication infrastructure components.