CVE-2017-17434 in rsync
Summary
by MITRE
The daemon in rsync 3.1.2, and 3.1.3-development before 2017-11-03, does not check for fnamecmp filenames in the daemon_filter_list data structure (in the recv_files function in receiver.c) and also does not apply the sanitize_paths protection mechanism to pathnames found in "xname follows" strings (in the read_ndx_and_attrs function in rsync.c), which allows remote attackers to bypass intended access restrictions.
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Analysis
by VulDB Data Team • 01/17/2023
The vulnerability identified as CVE-2017-17434 affects the rsync daemon component in versions 3.1.2 and 3.1.3-development prior to 2017-11-03, representing a critical security flaw in file synchronization software widely used across enterprise and network environments. This vulnerability resides within the daemon's handling of file path validation mechanisms, specifically impacting how the software processes filename comparisons and path sanitization. The flaw exists in two distinct code locations within the rsync codebase, creating multiple attack vectors that can be exploited by remote adversaries to circumvent access controls. The daemon_filter_list data structure in receiver.c contains a critical oversight where fnamecmp filenames are not properly validated, while the read_ndx_and_attrs function in rsync.c fails to apply sanitize_paths protection to "xname follows" strings, both of which contribute to the bypass of intended access restrictions.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization within the rsync daemon's core processing functions. When the daemon processes file synchronization requests, it fails to properly validate filenames stored in the daemon_filter_list data structure, allowing maliciously crafted filenames to bypass access control checks. Additionally, the software does not apply proper path sanitization to "xname follows" strings, which are typically used to store extended attribute information during file transfers. This dual failure creates a pathway for attackers to manipulate file paths and gain unauthorized access to resources that should be restricted. The vulnerability is classified under CWE-22, Improper Limitation of a Pathname to a Restricted Directory, and aligns with ATT&CK technique T1078.004 for Valid Accounts and T1566.001 for Spearphishing Attachment, as it enables privilege escalation through path manipulation.
The operational impact of CVE-2017-17434 extends beyond simple unauthorized file access, as it allows attackers to potentially execute arbitrary file operations within the target system's file hierarchy. Remote attackers can leverage this vulnerability to bypass directory restrictions, access sensitive files, and potentially execute malicious code through crafted file paths that would normally be rejected by the system's access control mechanisms. The vulnerability affects organizations using rsync daemon services, particularly those with exposed daemon ports or improperly configured access controls, making it a significant concern for network security administrators. Attackers can exploit this flaw to perform directory traversal attacks, access restricted file systems, and potentially establish persistent access to target environments. The vulnerability's exploitation requires minimal privileges and can be executed remotely, making it particularly dangerous in environments where rsync is configured to allow anonymous access or where access controls are not properly enforced.
Mitigation strategies for CVE-2017-17434 require immediate patching of affected rsync versions, with the recommended approach being the upgrade to rsync 3.1.3-development after 2017-11-03 or a stable release that includes the relevant security fixes. System administrators should also implement network segmentation to limit access to rsync daemon services, restrict access to specific IP addresses, and disable anonymous access where possible. Additional protective measures include implementing network monitoring to detect anomalous rsync traffic patterns, configuring proper access controls in rsync configuration files, and regularly auditing file access logs for suspicious activity. Organizations should also consider implementing network access controls and firewall rules to restrict access to rsync daemon ports, typically port 873, and ensure that only trusted systems can communicate with the daemon service. The vulnerability demonstrates the importance of proper input validation and path sanitization in network services, reinforcing the need for comprehensive security testing and code review processes for critical infrastructure software components.