CVE-2011-0281 in Kerberos
Summary
by MITRE
The unparse implementation in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) 1.6.x through 1.9, when an LDAP backend is used, allows remote attackers to cause a denial of service (file descriptor exhaustion and daemon hang) via a principal name that triggers use of a backslash escape sequence, as demonstrated by a \n sequence.
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Analysis
by VulDB Data Team • 12/29/2024
The vulnerability described in CVE-2011-0281 represents a critical denial of service flaw within the Key Distribution Center implementation of MIT Kerberos 5 version 1.6.x through 1.9 when utilizing an LDAP backend. This issue arises from improper handling of principal names containing backslash escape sequences during the unparse implementation process. The flaw specifically affects systems where Kerberos is configured to use LDAP as a backend storage mechanism for principal information, creating a pathway for remote attackers to exploit the service's parsing logic.
The technical root cause of this vulnerability lies in the insufficient validation and processing of escape sequences within principal names during the unparse operation performed by the KDC. When a specially crafted principal name containing backslash escape sequences is processed, the parsing logic enters an infinite loop or consumes excessive system resources, leading to file descriptor exhaustion and subsequent daemon hanging. This behavior stems from the KDC's failure to properly sanitize input data before processing, particularly when dealing with escape character sequences that are interpreted as part of the parsing algorithm rather than as literal characters within the principal name.
The operational impact of this vulnerability extends beyond simple service disruption, as it can effectively render the Kerberos authentication service completely unavailable to legitimate users. The file descriptor exhaustion occurs because the malformed principal name processing causes the daemon to continuously allocate and hold file descriptors without proper cleanup, eventually exhausting the system's available file descriptor limits. The daemon hang represents a more severe consequence where the service becomes unresponsive and requires manual intervention to restart, potentially disrupting authentication services across an entire domain or organization that relies on Kerberos for secure authentication.
This vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and demonstrates characteristics consistent with CWE-674, which covers uncontrolled resource consumption. The attack vector is particularly concerning as it requires only remote access to the Kerberos service to exploit, making it accessible to any attacker who can reach the KDC. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique for network denial of service, as it specifically targets the availability of network services through resource exhaustion. The vulnerability also reflects broader patterns in authentication system security where input sanitization failures can lead to cascading service disruptions.
Organizations utilizing MIT Kerberos 5 with LDAP backends should implement immediate mitigations including upgrading to versions 1.10 or later where this vulnerability has been addressed, implementing input validation controls at the network level to filter malformed principal names, and establishing monitoring for unusual file descriptor usage patterns. Additionally, administrators should consider implementing rate limiting and connection pooling mechanisms to reduce the impact of potential exploitation attempts. The fix typically involves proper handling of escape sequences in principal names and implementing robust input validation that prevents the parsing logic from entering resource-consuming loops when encountering malformed input data.