CVE-2005-0468 in Kerberos
Summary
by MITRE
Heap-based buffer overflow in the env_opt_add function in telnet.c for various BSD-based Telnet clients allows remote attackers to execute arbitrary code via responses that contain a large number of characters that require escaping, which consumers more memory than allocated.
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Analysis
by VulDB Data Team • 12/22/2024
The vulnerability identified as CVE-2005-0468 represents a critical heap-based buffer overflow affecting BSD-based telnet clients through the env_opt_add function in telnet.c. This flaw exists in the handling of telnet option negotiation responses where the application fails to properly validate the length of escaped character sequences. When a remote attacker crafts malicious telnet responses containing an excessive number of characters requiring escaping, the application allocates insufficient heap memory to accommodate the expanded data, creating a condition where subsequent memory writes overflow the allocated buffer boundaries. The vulnerability specifically targets the telnet protocol implementation in BSD systems, making it particularly dangerous for network infrastructure and administrative access points that rely on telnet for remote management.
The technical exploitation of this vulnerability occurs through the manipulation of telnet option negotiation sequences where escape characters are processed and expanded during the option handling phase. The env_opt_add function does not perform adequate bounds checking on the length of the escaped character data, allowing attackers to supply malformed responses that cause the heap allocator to allocate insufficient memory for the expanded content. When the application attempts to store the escaped character sequences, it writes beyond the allocated heap buffer, potentially overwriting adjacent memory structures including function pointers, return addresses, or other critical program data. This memory corruption can be leveraged by attackers to execute arbitrary code with the privileges of the telnet process, typically root or the user running the telnet client.
The operational impact of CVE-2005-0468 extends beyond simple privilege escalation as it affects the fundamental security posture of systems relying on telnet for remote access. Since telnet is commonly used for administrative access to network equipment, servers, and embedded devices, exploitation of this vulnerability can provide attackers with unauthorized access to critical infrastructure. The vulnerability affects multiple BSD-based implementations including FreeBSD, OpenBSD, and NetBSD systems, creating widespread exposure across network environments where these operating systems are deployed. The remote nature of the attack means that exploitation does not require local access to the target system, making it particularly dangerous for publicly accessible telnet services or systems that accept connections from untrusted networks.
Mitigation strategies for this vulnerability should focus on immediate patching of affected BSD implementations, as the original fix involved proper bounds checking and memory allocation validation within the env_opt_add function. System administrators should disable telnet services where possible and migrate to more secure alternatives such as ssh protocol implementations. Network segmentation and firewall rules should be implemented to restrict access to telnet services, particularly on systems where patching cannot be immediately deployed. The vulnerability aligns with CWE-121 heap-based buffer overflow category and represents a classic example of insufficient validation of input length, which maps to ATT&CK technique T1210 for exploitation of memory corruption vulnerabilities. Organizations should also implement network monitoring to detect malformed telnet option negotiation sequences that may indicate exploitation attempts, as this vulnerability can be used as a foothold for broader network compromise operations.