CVE-2009-3295 in Kerberos
Summary
by MITRE
The prep_reprocess_req function in kdc/do_tgs_req.c in the cross-realm referral implementation in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) 1.7 before 1.7.1 allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a ticket request.
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Analysis
by VulDB Data Team • 08/30/2021
The vulnerability identified as CVE-2009-3295 resides within the Key Distribution Center implementation of MIT Kerberos 5 version 1.7 before 1.7.1, specifically within the prep_reprocess_req function located in kdc/do_tgs_req.c. This function handles cross-realm referral operations, which are critical components in federated authentication systems where Kerberos realms communicate with each other to validate user credentials. The flaw manifests in the processing of ticket requests that involve cross-realm referrals, creating a potential attack vector that can be exploited by remote adversaries to disrupt the Kerberos authentication service.
The technical nature of this vulnerability stems from a NULL pointer dereference condition that occurs when the prep_reprocess_req function processes certain malformed or improperly constructed ticket requests. When a remote attacker crafts a specific type of ticket request that triggers the cross-realm referral code path, the function fails to properly validate pointer references before dereferencing them. This results in an immediate crash of the KDC daemon process, effectively causing a denial of service condition that prevents legitimate authentication requests from being processed. The vulnerability represents a classic software defect pattern that aligns with CWE-476, which specifically addresses NULL pointer dereference issues in software implementations.
The operational impact of this vulnerability extends beyond simple service disruption as it affects the fundamental authentication infrastructure that many enterprise systems rely upon. Organizations using MIT Kerberos 5 versions prior to 1.7.1 face significant risk of authentication service outages when attackers exploit this flaw, potentially leading to widespread access failures across systems that depend on Kerberos for secure authentication. The remote exploitation capability means that attackers do not need physical access or local privileges to trigger the vulnerability, making it particularly dangerous in networked environments where Kerberos services are exposed to external traffic. This vulnerability directly impacts the availability aspect of the CIA security triad and can be classified under the MITRE ATT&CK technique T1499.1, which involves disruption of services through denial of service attacks.
Mitigation strategies for this vulnerability primarily focus on immediate patching of affected systems to upgrade to MIT Kerberos 5 version 1.7.1 or later, which contains the necessary code fixes to properly handle cross-realm referral requests. System administrators should also implement network segmentation and access controls to limit exposure of KDC services to untrusted networks, while monitoring for suspicious authentication traffic patterns that might indicate exploitation attempts. Additional defensive measures include configuring intrusion detection systems to identify malformed ticket requests and implementing rate limiting on authentication requests to reduce the impact of potential exploitation attempts. Organizations should also review their cross-realm trust configurations to minimize the attack surface where this vulnerability could be exploited, ensuring that only necessary cross-realm referrals are enabled and properly secured.