CVE-2017-17433 in rsync
Summary
by MITRE
The recv_files function in receiver.c in the daemon in rsync 3.1.2, and 3.1.3-development before 2017-11-03, proceeds with certain file metadata updates before checking for a filename in the daemon_filter_list data structure, 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-2017-17433 represents a critical access control flaw in the rsync daemon implementation that affects versions 3.1.2 and 3.1.3-development prior to the 2017-11-03 release. This issue resides within the recv_files function located in receiver.c, which handles file transfer operations in the daemon mode of rsync. The flaw stems from an improper sequence of operations where the system updates file metadata before performing essential filename validation against the daemon_filter_list data structure. This temporal inconsistency creates a window where malicious actors can exploit the system's trust in the file transfer process to circumvent intended access controls that should prevent unauthorized file operations.
The technical nature of this vulnerability aligns with CWE-284, which describes improper access control mechanisms, and specifically demonstrates how inadequate input validation and improper privilege management can lead to security breaches. Attackers can leverage this flaw to bypass restrictions that should normally prevent access to specific files or directories through the rsync daemon interface. The vulnerability operates by allowing remote attackers to manipulate the file transfer process before the system validates whether the target filename should be accessible according to the configured filter rules, effectively enabling unauthorized file access or operations.
From an operational perspective, this vulnerability poses significant risks to systems running vulnerable rsync versions, particularly those exposed to untrusted networks or users. The impact extends beyond simple data access violations to potentially enable more severe attacks including data exfiltration, unauthorized file modifications, or privilege escalation within the context of the rsync daemon. Systems utilizing rsync for file synchronization, backup operations, or remote file access are particularly vulnerable when configured with daemon mode and access controls that rely on the daemon_filter_list functionality. The vulnerability essentially undermines the security model of the rsync daemon by allowing attackers to bypass the filtering mechanisms that should govern file access permissions.
Organizations should implement immediate mitigations including upgrading to rsync versions 3.1.3-development after 2017-11-03 or applying the relevant security patches that correct the order of operations in the recv_files function. Network segmentation and firewall rules should be implemented to restrict access to rsync daemon ports unless absolutely necessary, while also ensuring that daemon_filter_list configurations are properly maintained and validated. Additionally, monitoring for unusual file access patterns or unauthorized file transfers should be implemented to detect potential exploitation attempts. The ATT&CK framework categorizes this vulnerability under privilege escalation and defense evasion techniques, as it allows attackers to bypass established security controls and potentially escalate their access privileges within the affected systems.