CVE-2005-0469 in 3-DNS Controller
Summary
by MITRE
Buffer overflow in the slc_add_reply function in various BSD-based Telnet clients, when handling LINEMODE suboptions, allows remote attackers to execute arbitrary code via a reply with a large number of Set Local Character (SLC) commands.
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Analysis
by VulDB Data Team • 12/17/2024
The vulnerability identified as CVE-2005-0469 represents a critical buffer overflow flaw within BSD-based Telnet client implementations that specifically manifests when processing LINEMODE suboptions. This vulnerability resides in the slc_add_reply function which handles the Set Local Character (SLC) commands during Telnet protocol negotiations. The flaw occurs when remote attackers craft malicious Telnet responses containing an excessive number of SLC commands that exceed the allocated buffer space, triggering a classic buffer overflow condition that can be exploited to execute arbitrary code on vulnerable systems. The vulnerability affects multiple implementations of Telnet clients derived from BSD systems, making it particularly widespread across Unix-like operating environments.
The technical implementation of this vulnerability stems from inadequate input validation and buffer size management within the Telnet client's protocol handling code. When the slc_add_reply function processes incoming SLC commands during LINEMODE negotiation, it fails to properly validate the number of commands received or enforce strict buffer boundaries. This allows attackers to craft specially formatted Telnet replies that contain more SLC commands than the allocated buffer can accommodate, causing a stack-based buffer overflow. The overflow occurs because the function does not perform bounds checking on the incoming data stream, directly writing command data into a fixed-size buffer without verifying that the data length exceeds the buffer capacity. This flaw aligns with CWE-121, which categorizes stack-based buffer overflow conditions, and specifically demonstrates the dangerous combination of unchecked array indexing and insufficient input sanitization.
The operational impact of this vulnerability extends far beyond simple denial-of-service scenarios, as it provides attackers with the capability to execute arbitrary code with the privileges of the affected Telnet client process. This means that successful exploitation could allow remote attackers to gain unauthorized access to systems running vulnerable Telnet clients, potentially leading to complete system compromise. The vulnerability is particularly concerning because Telnet clients are commonly installed on servers and network devices, making them attractive targets for attackers seeking persistent access. Additionally, the nature of Telnet protocol usage means that exploitation can occur over standard network connections, requiring no special privileges or complex attack vectors beyond crafting the malicious reply packet. This vulnerability directly maps to ATT&CK technique T1075 which covers the use of legitimate credentials and network protocols for persistence and lateral movement.
Mitigation strategies for CVE-2005-0469 require immediate patching of vulnerable Telnet client implementations, with administrators prioritizing updates to their BSD-based systems. The most effective immediate solution involves applying vendor-specific patches that implement proper bounds checking and input validation within the slc_add_reply function. System administrators should also consider disabling Telnet services entirely where possible, as the protocol's inherent security weaknesses make it unsuitable for modern network environments. Network-level protections such as firewall rules that restrict Telnet access to trusted networks and intrusion detection systems that monitor for suspicious Telnet traffic patterns can provide additional layers of defense. Long-term remediation efforts should focus on migrating to more secure remote access protocols such as SSH, which provide built-in encryption and authentication mechanisms that eliminate the attack surface present in Telnet implementations. Organizations should also implement regular vulnerability assessments to identify other potentially vulnerable components within their network infrastructure that may be susceptible to similar buffer overflow conditions.