CVE-2017-15994 in rsync
Summary
by MITRE
rsync 3.1.3-development before 2017-10-24, as used in the xlucas svfs rsync fork and other products, mishandles archaic checksums, which makes it easier for remote attackers to bypass intended access restrictions.
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Analysis
by VulDB Data Team • 01/05/2023
The vulnerability identified as CVE-2017-15994 affects rsync versions 3.1.3-development prior to the 2017-10-24 release, specifically impacting the xlucas svfs rsync fork and related implementations. This issue represents a significant security flaw that undermines the integrity of access control mechanisms within the rsync protocol. The vulnerability stems from improper handling of archaic checksums, which creates opportunities for remote attackers to exploit the system and bypass intended access restrictions. The flaw exists in the checksum validation logic where legacy or outdated checksum formats are not properly rejected or handled, allowing malicious actors to manipulate the authentication process.
The technical implementation of this vulnerability resides in the checksum processing module of rsync, where the software fails to adequately validate checksum formats that are considered obsolete or archaic. This misconfiguration creates a path for attackers to submit specially crafted checksums that bypass normal validation procedures. The flaw operates at the protocol level, affecting how rsync handles data integrity verification during file synchronization operations. When rsync encounters these malformed checksums, it does not properly reject them according to established cryptographic standards, thereby allowing unauthorized access to resources that should be protected. The vulnerability is particularly concerning because it affects the core integrity verification mechanism that rsync relies upon to ensure data consistency and access control.
From an operational impact perspective, this vulnerability enables remote attackers to gain unauthorized access to systems running vulnerable versions of rsync, potentially leading to data compromise, privilege escalation, and unauthorized data modification. The attack vector is remote and does not require authentication to the system itself, making it particularly dangerous in networked environments where rsync is used for file synchronization. The vulnerability can be exploited to bypass access controls that are typically enforced during rsync operations, allowing attackers to access files and directories that should be restricted. This creates a significant risk for organizations that rely on rsync for data transfer and synchronization, as it undermines the fundamental security assumptions of the protocol.
The security implications of CVE-2017-15994 align with CWE-290 authentication bypass vulnerabilities and can be mapped to ATT&CK technique T1078 valid accounts, as attackers can leverage this flaw to gain access using legitimate but improperly validated authentication mechanisms. Organizations should implement immediate mitigations including updating to rsync version 3.1.3 or later, which contains the necessary fixes for checksum validation. Additional protective measures include network segmentation, firewall rules to restrict rsync access, and monitoring for unusual checksum validation patterns. The vulnerability demonstrates the importance of proper cryptographic protocol implementation and the need for robust input validation in security-critical applications, as highlighted in industry standards such as NIST SP 800-57 for cryptographic key management and OWASP top ten for authentication vulnerabilities.