CVE-2015-2694 in Kerberos
Summary
by MITRE
The kdcpreauth modules in MIT Kerberos 5 (aka krb5) 1.12.x and 1.13.x before 1.13.2 do not properly track whether a client's request has been validated, which allows remote attackers to bypass an intended preauthentication requirement by providing (1) zero bytes of data or (2) an arbitrary realm name, related to plugins/preauth/otp/main.c and plugins/preauth/pkinit/pkinit_srv.c.
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Analysis
by VulDB Data Team • 05/19/2022
The vulnerability identified as CVE-2015-2694 affects MIT Kerberos 5 versions 1.12.x and 1.13.x prior to 1.13.2, specifically within the kdcpreauth modules that handle preauthentication mechanisms. This flaw represents a critical security weakness in the Kerberos authentication system that undermines the integrity of the preauthentication process. The vulnerability stems from improper state tracking mechanisms within the preauthentication modules, particularly in the otp (one-time password) and pkinit (public key infrastructure) plugins, which are essential components for establishing secure authentication between clients and Key Distribution Centers. The issue manifests when the system fails to properly validate and track client authentication requests, creating a potential pathway for unauthorized access.
The technical implementation of this vulnerability occurs in the plugins/preauth/otp/main.c and plugins/preauth/pkinit/pkinit_srv.c files where the authentication state management becomes inconsistent. Attackers can exploit this by sending specially crafted requests containing either zero bytes of data or arbitrary realm names, effectively bypassing the intended preauthentication requirements. This exploitation technique leverages the lack of proper validation checks that should occur after initial authentication attempts, allowing malicious actors to circumvent the security controls designed to verify client legitimacy before granting access to Kerberos services. The flaw essentially creates a race condition or state inconsistency where the system cannot properly determine whether a client has successfully authenticated, leading to a false positive authentication state.
The operational impact of CVE-2015-2694 extends beyond simple unauthorized access, potentially enabling attackers to perform credential theft, privilege escalation, and lateral movement within networks that rely on Kerberos authentication. This vulnerability directly violates the fundamental security principle of authentication integrity, as defined by CWE-284, which addresses improper access control mechanisms. Organizations using affected Kerberos versions face significant risk of compromise since the flaw allows attackers to bypass critical security layers that protect against unauthorized network access. The vulnerability is particularly dangerous in enterprise environments where Kerberos serves as the primary authentication mechanism for single sign-on services, file servers, and other critical infrastructure components. Attackers can leverage this weakness to impersonate legitimate users and gain access to sensitive resources without proper authentication.
Mitigation strategies for CVE-2015-2694 require immediate patching of affected MIT Kerberos installations to version 1.13.2 or later, which contains the necessary fixes for proper preauthentication state tracking. Network administrators should also implement additional monitoring and logging mechanisms to detect anomalous authentication patterns that might indicate exploitation attempts. Security teams should review existing Kerberos configurations to ensure that preauthentication requirements are properly enforced and consider implementing additional authentication layers such as multi-factor authentication to reduce the impact of potential exploitation. The vulnerability demonstrates the importance of proper state management in security-critical systems and aligns with ATT&CK technique T1550.003, which covers use of Kerberos authentication protocols for privilege escalation and lateral movement. Organizations should also conduct thorough security assessments of their Kerberos implementations to identify any other potential state management issues that could create similar vulnerabilities in their authentication infrastructure.