CVE-2011-4862 in FreeBSD
Summary
by MITRE
Buffer overflow in libtelnet/encrypt.c in telnetd in FreeBSD 7.3 through 9.0, MIT Kerberos Version 5 Applications (aka krb5-appl) 1.0.2 and earlier, Heimdal 1.5.1 and earlier, GNU inetutils, and possibly other products allows remote attackers to execute arbitrary code via a long encryption key, as exploited in the wild in December 2011.
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Analysis
by VulDB Data Team • 07/15/2024
The CVE-2011-4862 vulnerability represents a critical buffer overflow flaw that affects multiple telnet implementations across different operating systems and security frameworks. This vulnerability specifically targets the libtelnet library's encryption handling component, where the telnet daemon fails to properly validate the length of encryption keys during the authentication process. The flaw manifests when a remote attacker sends a specially crafted, excessively long encryption key to a vulnerable telnet daemon, causing memory corruption that can be exploited to execute arbitrary code on the target system. The vulnerability was actively exploited in the wild during December 2011, demonstrating its real-world impact and the urgency of addressing such security flaws in network services.
The technical implementation of this vulnerability stems from improper bounds checking within the encryption key processing routine located in the encrypt.c file of the affected libtelnet implementations. When the telnet daemon receives an encryption key, it attempts to store this key in a fixed-size buffer without adequate validation of the key length. This allows attackers to overflow the allocated buffer space and overwrite adjacent memory locations, potentially including return addresses or function pointers. The flaw is categorized under CWE-121 as a stack-based buffer overflow, where insufficient bounds checking permits memory corruption that can be leveraged for privilege escalation or arbitrary code execution. The vulnerability affects multiple implementations including FreeBSD's telnetd service, MIT Kerberos Version 5 Applications, Heimdal implementations, and GNU inetutils, indicating a widespread issue within the telnet ecosystem.
The operational impact of CVE-2011-4862 extends beyond simple remote code execution, as it fundamentally compromises the security posture of systems relying on telnet services for remote access. Attackers can leverage this vulnerability to gain unauthorized access to systems, potentially escalating privileges to root level, and establish persistent backdoors within network infrastructure. The vulnerability's exploitation does not require authentication, making it particularly dangerous as it can be exploited against systems with default configurations or weak access controls. This aligns with ATT&CK technique T1021.004 for remote services and T1059.007 for command and scripting interpreter, as attackers can use the compromised telnet service to execute commands and maintain access to target systems. The widespread nature of the affected products means that organizations with legacy telnet implementations face significant risk exposure, particularly those with systems that have not been updated to patched versions.
Mitigation strategies for CVE-2011-4862 require immediate patching of all affected systems and implementations, with particular attention to the specific versions mentioned in the vulnerability description. Organizations should prioritize updating FreeBSD systems to versions 9.1 or later, upgrading MIT Kerberos applications to versions greater than 1.0.2, and updating Heimdal implementations beyond version 1.5.1. Additionally, system administrators should disable telnet services where possible and migrate to more secure alternatives such as SSH implementations. Network segmentation and firewall rules should be implemented to restrict access to telnet services, and monitoring should be enhanced to detect anomalous encryption key lengths or connection patterns that may indicate exploitation attempts. The vulnerability highlights the importance of maintaining up-to-date security patches and the risks associated with legacy network protocols that lack proper input validation and memory safety mechanisms.