CVE-2005-2040 in telnetd
Summary
by MITRE
Multiple buffer overflows in the getterminaltype function in telnetd for Heimdal before 0.6.5 may allow remote attackers to execute arbitrary code, a different vulnerability than CVE-2005-0468 and CVE-2005-0469.
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Analysis
by VulDB Data Team • 06/02/2019
The vulnerability described in CVE-2005-2040 represents a critical buffer overflow condition affecting the telnetd service implementation within the Heimdal Kerberos software suite. This flaw specifically resides in the getterminaltype function, which is responsible for determining and processing terminal type information during telnet connections. The vulnerability manifests when the telnetd daemon processes incoming terminal type requests from remote clients without proper bounds checking on user-supplied input data. This particular implementation flaw creates a scenario where maliciously crafted terminal type information can cause the application to write beyond the allocated memory boundaries, potentially leading to arbitrary code execution on the affected system.
The technical nature of this vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The flaw operates through the standard telnet protocol communication channels, where clients send terminal type information as part of their connection negotiation process. When the getterminaltype function fails to properly validate the length of incoming terminal type strings, it becomes susceptible to buffer overflow attacks that can be exploited remotely. This vulnerability is distinct from the related CVE-2005-0468 and CVE-2005-0469, indicating that it represents a separate code path or implementation issue within the Heimdal telnetd component.
The operational impact of this vulnerability is severe and potentially catastrophic for systems running affected versions of Heimdal Kerberos. Remote attackers who successfully exploit this buffer overflow can gain arbitrary code execution privileges on the target system, potentially escalating their access to full system control. The attack requires only network connectivity to the telnetd service, making it particularly dangerous as it can be exploited from anywhere on the network. Successful exploitation could result in complete system compromise, data exfiltration, or the establishment of persistent backdoors within the network infrastructure. Organizations relying on telnet services for authentication and remote access would be particularly vulnerable, as the attack vector does not require any special privileges or local access.
Mitigation strategies for this vulnerability should focus on immediate patch application to upgrade to Heimdal version 0.6.5 or later, which contains the necessary fixes for the buffer overflow condition. Network administrators should also implement firewall rules to restrict access to telnet services where possible, as the service is inherently insecure and should be replaced with more secure alternatives such as SSH. Additionally, monitoring for unusual telnet connection patterns and terminal type information requests can help detect potential exploitation attempts. System hardening measures including address space layout randomization and stack canaries should be implemented to reduce the effectiveness of potential exploitation attempts. From an operational security perspective, organizations should conduct comprehensive vulnerability assessments to identify all systems running affected Heimdal versions and ensure proper patch management procedures are in place to prevent similar issues in the future. The vulnerability demonstrates the importance of input validation and proper memory management practices in network services, aligning with ATT&CK technique T1190 for exploitation through buffer overflow conditions and T1071 for application layer protocols.