CVE-2001-0094 in Kerberos
Summary
by MITRE
Buffer overflow in kdc_reply_cipher of libkrb (Kerberos 4 authentication library) in NetBSD 1.5 and FreeBSD 4.2 and earlier, as used in Kerberised applications such as telnetd and login, allows local users to gain root privileges.
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Analysis
by VulDB Data Team • 05/30/2019
The vulnerability identified as CVE-2001-0094 represents a critical buffer overflow flaw within the Kerberos 4 authentication library implementation in Unix-like operating systems. This issue specifically affects the kdc_reply_cipher function within libkrb, which serves as a core component of the Kerberos authentication mechanism used to secure network services. The vulnerability manifests in NetBSD 1.5 and FreeBSD 4.2 and earlier versions, where the improper handling of cryptographic reply buffers creates exploitable conditions that can be leveraged by local attackers to escalate privileges to root level access. The affected applications include telnetd and login services, which are fundamental network authentication tools that rely on Kerberos 4 for secure user authentication.
The technical flaw stems from inadequate bounds checking within the kdc_reply_cipher function, which processes encrypted responses from Kerberos key distribution centers. When the function receives a malformed or oversized cryptographic reply, it fails to validate the buffer size before copying data into a fixed-length buffer structure. This classic buffer overflow condition occurs because the implementation does not properly verify that incoming data fits within allocated memory boundaries, allowing an attacker to overwrite adjacent memory locations including return addresses and control data. The vulnerability is particularly dangerous because it operates within the authentication subsystem where local users already have some level of system access, making privilege escalation possible through carefully crafted inputs that trigger the overflow condition.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential system compromise and unauthorized access to sensitive network services. Local users who can execute code on the target system can exploit this flaw to gain root privileges, effectively bypassing all security controls that depend on proper authentication. The attack vector is particularly concerning for network services like telnetd and login that are commonly used for remote administration, as an attacker with local access could use this vulnerability to obtain complete system control. This vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a classic example of how authentication system flaws can be exploited to achieve unauthorized privilege escalation. The impact is further amplified by the fact that these vulnerable systems were widely deployed in enterprise environments where network services rely heavily on Kerberos authentication.
Mitigation strategies for CVE-2001-0094 require immediate system updates and patches to address the buffer overflow condition in the libkrb library. System administrators should prioritize upgrading to patched versions of NetBSD 1.5 and FreeBSD 4.2 or later, which contain corrected implementations of the kdc_reply_cipher function with proper input validation. Additionally, security hardening measures including disabling unnecessary network services, implementing proper access controls, and monitoring for suspicious authentication attempts should be implemented. The vulnerability demonstrates the importance of input validation in cryptographic libraries and aligns with ATT&CK technique T1068, which covers local privilege escalation through exploitation of system vulnerabilities. Organizations should also consider implementing network segmentation and privilege separation to limit the potential impact of such vulnerabilities, while maintaining regular security assessments to identify similar flaws in authentication subsystems. The remediation process should include comprehensive testing to ensure that patched implementations do not introduce regressions in legitimate authentication functionality while maintaining the security improvements necessary to prevent exploitation.