CVE-2017-8805 in ftpsync
Summary
by MITRE
Debian ftpsync before 20171017 does not use the rsync --safe-links option, which allows remote attackers to conduct directory traversal attacks via a crafted upstream mirror.
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Analysis
by VulDB Data Team • 01/03/2023
The vulnerability identified as CVE-2017-8805 affects Debian ftpsync versions prior to 20171017 and represents a critical directory traversal flaw that can be exploited by remote attackers. This issue specifically impacts the ftpsync utility which is used to synchronize Debian package repositories from upstream mirrors. The vulnerability stems from the absence of the rsync --safe-links option during synchronization operations, creating a pathway for malicious actors to manipulate file paths and access unauthorized directories on the target system. The flaw enables attackers to traverse the file system hierarchy and potentially access sensitive files or directories that should remain protected.
The technical implementation of this vulnerability occurs within the rsync command execution process where ftpsync performs repository synchronization. Without the --safe-links option, rsync does not properly handle symbolic links that point outside the target directory, allowing attackers to craft malicious upstream mirror configurations that contain symbolic links referencing arbitrary file paths. This creates a condition where the synchronization process can inadvertently copy or reference files from locations outside the intended repository structure. The vulnerability specifically relates to CWE-22 which defines path traversal or directory traversal flaws that allow attackers to access files and directories outside the intended scope of the application. When an attacker controls the upstream mirror content, they can create symbolic links that point to sensitive system files, configuration data, or other restricted resources that would normally be inaccessible through standard repository operations.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more serious compromise scenarios. Attackers who successfully exploit this vulnerability can access system configuration files, log files, or other sensitive data that might contain credentials, system information, or other valuable intelligence. In environments where ftpsync is used to maintain multiple repository mirrors, the attack surface expands significantly as attackers can potentially compromise the synchronization process across multiple systems. The vulnerability also aligns with ATT&CK technique T1083 which covers directory and file system discovery, as successful exploitation would allow attackers to enumerate and access files and directories that should remain protected. Organizations using Debian ftpsync without the proper rsync safety measures face a heightened risk of unauthorized access to critical system resources.
Mitigation strategies for CVE-2017-8805 focus primarily on updating to the patched version of ftpsync released after 20171017, which properly implements the rsync --safe-links option. System administrators should also implement additional security measures such as validating upstream mirror configurations and monitoring for suspicious symbolic link creation in repository directories. Network segmentation and access controls should be enforced to limit which systems can interact with ftpsync processes and upstream mirrors. Regular security audits of repository synchronization processes should include verification that rsync options are properly configured and that no unauthorized symbolic links exist in repository structures. Organizations should also consider implementing automated monitoring for changes to repository contents that might indicate exploitation attempts, particularly around symbolic link creation or modification in sensitive directories. The fix ensures that rsync properly handles symbolic links by preventing them from pointing outside the target directory, thereby eliminating the directory traversal pathway that attackers could exploit to access unauthorized files and directories.