CVE-2004-0640 in Secure Telnet
Summary
by MITRE
Format string vulnerability in the SSL_set_verify function in telnetd.c for SSLtelnet daemon (SSLtelnetd) 0.13 allows remote attackers to execute arbitrary code.
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Analysis
by VulDB Data Team • 06/02/2019
The vulnerability identified as CVE-2004-0640 represents a critical format string flaw within the SSLtelnetd daemon version 0.13, specifically within the SSL_set_verify function located in the telnetd.c source file. This vulnerability arises from improper handling of user-supplied input during string formatting operations, creating an exploitable condition that can be leveraged by remote attackers to execute arbitrary code on affected systems. The SSLtelnetd daemon serves as a secure telnet implementation that combines telnet functionality with ssl encryption, making it a target for attackers seeking to compromise network access and execute malicious payloads.
The technical flaw manifests when the SSL_set_verify function processes input parameters without proper validation or sanitization of format specifiers. When remote attackers supply malicious input containing format string sequences such as %x, %s, or %n, the function fails to properly escape these characters before passing them to underlying string formatting functions. This improper input handling allows attackers to manipulate the stack, potentially leading to information disclosure, application crashes, or more critically, arbitrary code execution. The vulnerability is classified under CWE-134 as "Use of Externally-Controlled Format String," which specifically addresses the risks associated with allowing external input to control format string parameters in printf-like functions.
The operational impact of this vulnerability extends beyond simple remote code execution, as it can enable attackers to gain unauthorized access to systems running vulnerable SSLtelnetd implementations. Attackers can exploit this flaw to inject malicious code that executes with the privileges of the SSLtelnetd process, potentially leading to complete system compromise. The remote nature of the attack means that exploitation can occur from any location on the network, making this vulnerability particularly dangerous for systems exposed to untrusted networks. Network administrators should be aware that successful exploitation could result in persistent backdoors, data exfiltration, or further lateral movement within compromised networks, as the attacker gains a foothold with elevated privileges.
Mitigation strategies for CVE-2004-0640 should prioritize immediate patching of the SSLtelnetd daemon to version 0.14 or later, which contains the necessary fixes for the format string vulnerability. System administrators should also implement network segmentation and access controls to limit exposure of vulnerable services to untrusted networks. Additionally, monitoring for suspicious network traffic patterns and implementing intrusion detection systems can help identify exploitation attempts. The remediation process should include thorough testing of patched implementations to ensure that the fix does not introduce regressions in functionality while maintaining the security posture of affected systems. Organizations should also consider implementing application-level firewalls or proxy solutions to further protect vulnerable services from direct network access.