CVE-2006-1951 in TFTP Server
Summary
by MITRE
Directory traversal vulnerability in SolarWinds TFTP Server 8.1 and earlier allows remote attackers to download arbitrary files via a crafted GET request including "....//" sequences, which are collapsed into "../" sequences by filtering.
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Analysis
by VulDB Data Team • 09/08/2017
The vulnerability identified as CVE-2006-1951 represents a critical directory traversal flaw within SolarWinds TFTP Server version 8.1 and earlier implementations. This security weakness stems from inadequate input validation mechanisms that fail to properly sanitize file path requests submitted through the TFTP protocol. The vulnerability specifically manifests when attackers craft malicious GET requests containing "....//" sequences that are subsequently processed and collapsed by the server's filtering mechanisms into standard "../" directory traversal sequences. This fundamental flaw in path normalization logic creates an exploitable condition that bypasses intended security controls designed to prevent unauthorized access to system files.
The technical implementation of this vulnerability operates through a sophisticated manipulation of the TFTP protocol's file retrieval mechanism. When the SolarWinds TFTP Server receives a GET request containing the crafted "....//" sequences, its internal filtering logic processes these inputs and transforms them into conventional "../" traversal patterns that the system interprets as legitimate navigation commands. This transformation occurs within the server's path resolution component, where the filtering mechanism fails to properly distinguish between benign and malicious path traversal attempts. The vulnerability is categorized under CWE-22, which specifically addresses Improper Limitation of a Pathname to a Restricted Directory, commonly known as Path Traversal or Directory Traversal attacks. This classification aligns with the fundamental principle that applications should validate and sanitize all file path inputs to prevent unauthorized access to system resources.
The operational impact of this vulnerability extends far beyond simple unauthorized file access, creating significant risks for organizations relying on SolarWinds TFTP Server implementations. Remote attackers can leverage this weakness to access sensitive system files, configuration data, and potentially execute arbitrary code within the server environment. The vulnerability enables attackers to bypass standard access controls and retrieve files that should remain restricted, including system binaries, configuration files, and potentially sensitive user data. From an adversary perspective, this represents a critical privilege escalation opportunity that can lead to complete system compromise. The attack vector requires no authentication and can be executed remotely, making it particularly dangerous in networked environments where TFTP servers are exposed to untrusted networks. The vulnerability aligns with ATT&CK technique T1071.004, which covers Application Layer Protocol: DNS, but more specifically relates to T1083, File and Directory Discovery, and T1005, Data from Local System, as attackers can systematically enumerate and extract sensitive data from the affected server.
Mitigation strategies for CVE-2006-1951 must address both immediate remediation and long-term architectural improvements to prevent similar vulnerabilities. The primary solution involves upgrading to SolarWinds TFTP Server versions that have addressed this directory traversal flaw through proper input validation and sanitization mechanisms. Organizations should implement comprehensive network segmentation to limit exposure of TFTP servers to untrusted networks, ensuring these services operate within protected network zones. Additionally, implementing strict access controls and authentication mechanisms can help reduce the attack surface, although these measures alone are insufficient to prevent this specific vulnerability. The solution requires robust input validation that properly handles and rejects all forms of path traversal sequences regardless of their encoding or representation. Security professionals should also consider implementing network monitoring and intrusion detection systems to detect anomalous TFTP traffic patterns that may indicate exploitation attempts. From a compliance perspective, this vulnerability highlights the importance of maintaining up-to-date software versions and implementing proper security testing procedures, including penetration testing and vulnerability scanning, to identify and remediate similar issues before they can be exploited by malicious actors.