CVE-2018-5764 in rsync
Summary
by MITRE
The parse_arguments function in options.c in rsyncd in rsync before 3.1.3 does not prevent multiple --protect-args uses, which allows remote attackers to bypass an argument-sanitization protection mechanism.
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Analysis
by VulDB Data Team • 02/02/2023
The vulnerability described in CVE-2018-5764 affects the rsync daemon implementation in versions prior to 3.1.3, specifically within the parse_arguments function located in options.c. This flaw represents a critical security issue that undermines the integrity of argument sanitization mechanisms designed to prevent command injection attacks. The vulnerability stems from the improper handling of command-line arguments where the --protect-args option can be specified multiple times without proper validation. This allows attackers to circumvent the intended protection mechanisms that are meant to sanitize and validate input arguments before they are processed by the rsync daemon. The flaw exists in the argument parsing logic where the system fails to detect or reject duplicate occurrences of the protect-args flag, thereby enabling malicious actors to manipulate the argument processing flow.
The technical exploitation of this vulnerability occurs through a specific pattern of command-line argument manipulation that bypasses the argument sanitization protection. When rsyncd processes multiple instances of --protect-args, the parsing function does not properly validate or count these occurrences, allowing an attacker to effectively disable or override the sanitization protections that would normally prevent dangerous argument sequences from being executed. This behavior creates a path for remote attackers to inject malicious arguments that would otherwise be filtered out by the protection mechanism. The flaw directly relates to CWE-121, which describes buffer overflow conditions where insufficient validation of input arguments leads to improper memory handling and potential code execution. The vulnerability operates at the command-line argument parsing layer, making it particularly dangerous as it can be exploited during the daemon startup or configuration phases where arguments are processed.
The operational impact of this vulnerability extends beyond simple bypass of protection mechanisms to potentially enable remote code execution or privilege escalation within the rsync daemon environment. Attackers can leverage this flaw to inject malicious arguments that may be executed with the privileges of the rsync daemon process, which typically runs with elevated permissions to access and synchronize files across systems. The vulnerability affects any system running rsyncd versions before 3.1.3, making it particularly concerning for network services that rely on rsync for file synchronization and backup operations. From an attacker perspective, this vulnerability aligns with ATT&CK technique T1059.001 for command and script injection, as it allows for manipulation of command-line arguments that are then processed by the target system. The impact is significant because rsync is commonly used in enterprise environments for critical file synchronization tasks, making this vulnerability a prime target for exploitation in privilege escalation attacks.
Mitigation strategies for CVE-2018-5764 primarily focus on upgrading to rsync version 3.1.3 or later where the argument parsing logic has been corrected to properly validate multiple instances of the --protect-args option. System administrators should immediately implement this upgrade across all affected rsync daemon installations, particularly in production environments where the daemon is exposed to untrusted networks. Additionally, network segmentation and firewall rules should be implemented to limit access to rsync daemon services to trusted hosts only, reducing the attack surface for remote exploitation attempts. The vulnerability highlights the importance of proper input validation and argument sanitization in network services, demonstrating how seemingly minor parsing flaws can have significant security implications. Organizations should also implement monitoring and logging for rsync daemon processes to detect unusual argument patterns that might indicate exploitation attempts. The fix implemented in version 3.1.3 addresses the root cause by ensuring that duplicate --protect-args specifications are properly rejected or handled, thereby restoring the intended security protections for argument processing within the rsync daemon implementation.