CVE-2011-1530 in Kerberos
Summary
by MITRE
The process_tgs_req function in do_tgs_req.c in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) 1.9 through 1.9.2 allows remote authenticated users to cause a denial of service (NULL pointer dereference and daemon crash) via a crafted TGS request that triggers an error other than the KRB5_KDB_NOENTRY error.
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Analysis
by VulDB Data Team • 01/13/2025
The vulnerability identified as CVE-2011-1530 represents a critical denial of service weakness within the MIT Kerberos 5 implementation that affects versions 1.9 through 1.9.2. This flaw exists in the process_tgs_req function located within the do_tgs_req.c file of the Key Distribution Center component, which serves as the central authentication service in Kerberos environments. The vulnerability specifically targets the Ticket Granting Service request processing mechanism that handles authentication requests for network services. When a remote authenticated user submits a specially crafted TGS request, the system fails to properly validate the request parameters, leading to a NULL pointer dereference that ultimately causes the KDC daemon to crash and terminate its operations.
The technical nature of this vulnerability stems from inadequate error handling within the Kerberos authentication process. The process_tgs_req function does not properly account for all possible error conditions that can occur during TGS request processing, particularly when encountering error states other than KRB5_KDB_NOENTRY. This oversight creates a scenario where a malformed request can trigger a NULL pointer dereference, a common programming error that occurs when software attempts to access memory through a pointer that has not been properly initialized or has been set to null. The flaw operates at the protocol level where Kerberos handles authentication tokens and service tickets, making it particularly dangerous as it can be exploited by any authenticated user within the Kerberos realm. This vulnerability directly maps to CWE-476 which describes NULL pointer dereference conditions in software implementations.
The operational impact of CVE-2011-1530 extends beyond simple service disruption as it can severely compromise the availability of authentication services within a Kerberos environment. When the KDC daemon crashes, all users within that realm lose access to authentication services, effectively creating a denial of service condition that can impact enterprise networks, cloud environments, and any system relying on Kerberos for secure authentication. The vulnerability is particularly concerning because it requires only authenticated access to exploit, meaning that an attacker with legitimate credentials could potentially disrupt services for the entire domain. This makes the attack surface broader than typical denial of service vulnerabilities and aligns with ATT&CK technique T1499.004 which covers network denial of service attacks targeting authentication services. Organizations relying on Kerberos for single sign-on, service authentication, and secure network access would experience significant operational disruption when this vulnerability is exploited.
Mitigation strategies for CVE-2011-1530 should prioritize immediate patching of affected Kerberos implementations to version 1.9.3 or later where the vulnerability has been addressed through proper error handling mechanisms. System administrators should also implement monitoring solutions to detect unusual patterns in TGS request processing that might indicate exploitation attempts. Network segmentation and access controls should be enforced to limit the potential impact of successful exploitation attempts. Additionally, organizations should consider implementing redundant authentication services and failover mechanisms to maintain availability during potential exploitation events. The fix for this vulnerability demonstrates the importance of proper error handling in security-critical code and emphasizes the need for comprehensive testing of edge cases in authentication protocols, particularly those handling sensitive ticketing operations within enterprise security infrastructures.