CVE-2010-1321 in Kerberos
Summary
by MITRE
The kg_accept_krb5 function in krb5/accept_sec_context.c in the GSS-API library in MIT Kerberos 5 (aka krb5) through 1.7.1 and 1.8 before 1.8.2, as used in kadmind and other applications, does not properly check for invalid GSS-API tokens, which allows remote authenticated users to cause a denial of service (NULL pointer dereference and daemon crash) via an AP-REQ message in which the authenticator s checksum field is missing.
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Analysis
by VulDB Data Team • 09/13/2021
The vulnerability described in CVE-2010-1321 represents a critical flaw in the MIT Kerberos 5 implementation that affects the GSS-API library's handling of authentication tokens. This issue specifically targets the kg_accept_krb5 function located in krb5/accept_sec_context.c, which serves as a core component in the Kerberos authentication process. The vulnerability manifests when the system processes AP-REQ messages containing malformed authenticator checksum fields, creating a scenario where the application fails to validate the integrity of incoming authentication tokens before attempting to process them. This flaw exists in versions through 1.7.1 and 1.8 before 1.8.2, making it a widespread issue affecting numerous Kerberos implementations that rely on these specific library components.
The technical exploitation of this vulnerability occurs through a specific sequence of events involving the GSS-API token validation process. When an authenticated user sends an AP-REQ message with a missing checksum field in the authenticator portion, the kg_accept_krb5 function fails to properly validate this malformed token before attempting to dereference a null pointer. This null pointer dereference causes the kadmind daemon or other affected applications to crash immediately, resulting in a denial of service condition that can be exploited by authenticated attackers to disrupt Kerberos services. The vulnerability stems from inadequate input validation and error handling within the token processing pipeline, where the system assumes the presence of valid checksum data without proper verification.
From an operational perspective, this vulnerability poses significant risks to Kerberos-based authentication systems that rely on the affected MIT Kerberos implementations. The denial of service impact extends beyond simple daemon crashes to potentially compromise the entire authentication infrastructure, as kadmind services are critical for managing Kerberos principals and key distribution. Organizations utilizing Kerberos for single sign-on, network authentication, and service access control face substantial operational disruption when this vulnerability is exploited. The authenticated nature of the attack means that adversaries must already possess valid credentials to exploit the vulnerability, but this requirement does not mitigate the potential damage, as successful exploitation can lead to persistent service unavailability and increased administrative overhead for system recovery and monitoring.
The vulnerability aligns with CWE-476, which describes NULL pointer dereference conditions in software implementations, and represents a classic example of improper input validation within security-critical code paths. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique involving network denial of service, and potentially to T1566.001 for credential access through manipulation of authentication protocols. The exploitability characteristics make this a particularly dangerous vulnerability in environments where Kerberos is heavily relied upon, as the crash can occur without extensive reconnaissance or specialized tools. Organizations should prioritize patching affected systems to address this vulnerability, as the impact of a successful attack can extend far beyond immediate service disruption to compromise overall system security posture and availability.
Mitigation strategies for this vulnerability include immediate deployment of patches released by MIT Kerberos for versions 1.7.2 and 1.8.2, which address the improper validation of GSS-API tokens. System administrators should also implement monitoring solutions to detect unusual patterns of authentication failures or daemon crashes that might indicate exploitation attempts. Network segmentation and access controls can help limit the impact of successful exploitation by restricting which authenticated users can reach vulnerable services. Additionally, implementing proper logging and alerting mechanisms around Kerberos authentication services will enable administrators to quickly identify and respond to potential exploitation attempts, while regular security audits of Kerberos configurations can help identify other potential vulnerabilities in the authentication infrastructure.