CVE-2008-6899 in FreeSSHD
Summary
by MITRE
Multiple buffer overflows in freeSSHd 1.2.1 allow remote authenticated users to cause a denial of service (crash) and execute arbitrary code via a long (1) open, (2) unlink, (3) mkdir, (4) rmdir, or (5) stat SFTP command.
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Analysis
by VulDB Data Team • 05/24/2025
The vulnerability identified as CVE-2008-6899 represents a critical security flaw in freeSSHd version 1.2.1 that exposes multiple buffer overflow conditions within the SFTP implementation. This issue affects the core file system operations that are fundamental to secure file transfer protocols, making it particularly dangerous for systems that rely on SFTP for remote file management. The vulnerability specifically targets five distinct SFTP commands including open, unlink, mkdir, rmdir, and stat, all of which are essential operations for file system management within the SSH protocol framework. These buffer overflows occur when the application fails to properly validate input lengths before processing SFTP commands, creating opportunities for malicious exploitation.
The technical nature of this vulnerability stems from improper boundary checking within the SFTP server implementation where fixed-size buffers are used to store command parameters without adequate length validation. When authenticated users send SFTP commands containing excessively long parameter strings, the application's buffer management fails to handle the overflow gracefully, leading to memory corruption that can result in application crashes or more severe exploitation outcomes. This type of vulnerability maps directly to CWE-121, which describes heap-based buffer overflow conditions, and CWE-122, which covers stack-based buffer overflow scenarios that can occur in similar network service implementations. The flaw demonstrates poor input validation practices that violate fundamental security principles for network service development.
The operational impact of CVE-2008-6899 extends beyond simple denial of service conditions to encompass potential remote code execution capabilities that could allow attackers to gain complete control over affected systems. This vulnerability affects systems running freeSSHd 1.2.1 where SFTP functionality is enabled, potentially compromising servers that handle sensitive data transfers or serve as critical infrastructure components. The authenticated nature of the attack means that an attacker must first obtain valid credentials, but once achieved, they can leverage this vulnerability to either crash the SFTP service or execute arbitrary code with the privileges of the SFTP service account. This represents a significant risk in environments where SFTP is used for automated file transfers or where the service runs with elevated privileges.
Mitigation strategies for this vulnerability should prioritize immediate patching of affected freeSSHd installations to version 1.2.2 or later, which contains the necessary buffer overflow protections. Organizations should also implement network segmentation and access controls to limit exposure of SFTP services to authenticated users only, while monitoring for suspicious SFTP activity that might indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1078 which covers valid accounts and T1059 which covers command and scripting interpreter, as attackers could use this vulnerability to establish persistent access through command execution capabilities. Additionally, implementing proper input validation and bounds checking in all network service implementations can prevent similar issues, with recommendations to follow secure coding practices such as those outlined in the CERT Secure Coding Standards and OWASP Secure Coding Practices. System administrators should also consider disabling unnecessary SFTP commands or implementing rate limiting to reduce the attack surface while maintaining essential functionality.