CVE-2017-6805 in MobaXterm Personal Edition
Summary
by MITRE
Directory traversal vulnerability in the TFTP server in MobaXterm Personal Edition 9.4 allows remote attackers to read arbitrary files via a .. (dot dot) in a GET command.
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Analysis
by VulDB Data Team • 09/09/2020
The vulnerability identified as CVE-2017-6805 represents a critical directory traversal flaw within the TFTP server component of MobaXterm Personal Edition version 9.4. This vulnerability exposes the underlying system to unauthorized file access through a seemingly simple manipulation of TFTP commands. The flaw specifically manifests when a remote attacker crafts a GET command containing directory traversal sequences using the .. (dot dot) notation, enabling them to access files outside the intended directory structure. Such a vulnerability fundamentally undermines the security boundaries established by the TFTP server implementation.
The technical exploitation of this vulnerability stems from inadequate input validation within the TFTP server's file path handling mechanism. When processing GET requests, the server fails to properly sanitize or canonicalize file paths before attempting to access the requested files. This allows attackers to inject directory traversal sequences that bypass normal access controls and navigate to arbitrary locations within the file system. The vulnerability aligns with CWE-22, which classifies directory traversal or path traversal attacks as a common weakness in software applications. The flaw essentially permits attackers to perform a form of file system traversal that should be restricted by proper access control mechanisms.
Operationally, this vulnerability poses significant risks to systems running the affected MobaXterm version, particularly in environments where the TFTP server is enabled. Remote attackers can leverage this weakness to access sensitive files including configuration data, user credentials, system logs, and potentially even system binaries. The impact extends beyond simple information disclosure as attackers could potentially access files containing authentication tokens, private keys, or other confidential data that could facilitate further exploitation. The vulnerability is particularly concerning in enterprise environments where MobaXterm might be used for remote administration tasks, as it could enable attackers to escalate privileges or gain unauthorized access to critical system resources.
The security implications of this vulnerability extend to multiple ATT&CK framework techniques including T1083 (File and Directory Discovery) and T1071.1 (Application Layer Protocol: File Transfer Protocol). Attackers could use this vulnerability as a reconnaissance tool to map the target file system structure, identify sensitive files, and potentially discover additional attack vectors. The vulnerability also enables T1566 (Phishing) and T1562.001 (Impair Defenses: Disable or Modify Tools) by allowing attackers to access system tools and configurations that might be used to further compromise the target environment. Organizations should consider this vulnerability as part of a broader attack surface assessment, particularly in environments where TFTP services are exposed to untrusted networks.
Mitigation strategies for CVE-2017-6805 should prioritize immediate software updates to versions that address the directory traversal vulnerability. System administrators should disable the TFTP server component in MobaXterm if it is not actively required for legitimate use cases. Network segmentation and firewall rules should be implemented to restrict access to TFTP services to only trusted network segments. Additionally, regular security audits should be conducted to identify and remediate similar vulnerabilities in other network services. The vulnerability highlights the importance of proper input validation and access control implementation in network services, and organizations should review their security practices to prevent similar weaknesses in other applications and services.