CVE-2002-2443 in Kerberos
Summary
by MITRE
schpw.c in the kpasswd service in kadmind in MIT Kerberos 5 (aka krb5) before 1.11.3 does not properly validate UDP packets before sending responses, which allows remote attackers to cause a denial of service (CPU and bandwidth consumption) via a forged packet that triggers a communication loop, as demonstrated by krb_pingpong.nasl, a related issue to CVE-1999-0103.
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Analysis
by VulDB Data Team • 01/03/2022
The vulnerability identified as CVE-2002-2443 resides within the kpasswd service of MIT Kerberos 5 implementation, specifically in the schpw.c component that handles password changes. This flaw affects versions prior to 1.11.3 and represents a critical security weakness in the Kerberos authentication infrastructure that underpins many enterprise network security systems. The vulnerability manifests through improper validation of UDP packets received by the kadmind service, which operates as the key distribution center responsible for managing user credentials and authentication tokens within Kerberos realms.
The technical exploitation of this vulnerability occurs when remote attackers craft forged UDP packets that exploit the lack of proper input validation in the schpw.c module. These malicious packets trigger a communication loop within the kpasswd service, causing the system to continuously process and respond to malformed requests without proper termination conditions. The attack vector specifically targets the UDP protocol implementation where the service fails to validate packet integrity and source authenticity before processing responses. This communication loop results in excessive CPU utilization as the system becomes trapped in continuous processing cycles, while simultaneously consuming significant network bandwidth through the repetitive transmission of response packets.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially compromise entire Kerberos realms and the authentication infrastructure they support. When exploited, the vulnerability can cause cascading failures throughout network services that depend on Kerberos authentication, affecting authentication servers, client applications, and any systems relying on the compromised kadmind service. The attack demonstrates characteristics consistent with CWE-129, Input Validation, and aligns with ATT&CK technique T1498.001 for Denial of Service through resource exhaustion. Network monitoring systems may detect unusual traffic patterns and CPU spikes, but the forged packet nature makes detection challenging as the traffic appears legitimate to basic network inspection tools.
Mitigation strategies for CVE-2002-2443 require immediate patching of affected MIT Kerberos 5 installations to version 1.11.3 or later, which contains the necessary input validation fixes. Organizations should also implement network-level protections such as UDP packet filtering and rate limiting on the kpasswd service ports, typically UDP 464. The implementation of proper packet validation mechanisms within the kadmind service configuration can help reduce attack surface, while network segmentation can limit the potential impact of successful exploitation attempts. Security teams should monitor for signs of exploitation through anomalous CPU usage patterns and unusual network traffic, particularly focusing on UDP traffic to Kerberos service ports. Additionally, implementing proper access controls and authentication for the kpasswd service can help prevent unauthorized exploitation attempts while maintaining service availability for legitimate users.