CVE-2026-53788 in rsync
Summary
by MITRE • 08/13/2026
rsync before 3.5.0 contains a newline injection vulnerability in the name-converter uid/gid mapping interface that allows local attackers to forge protocol messages by creating user or group names containing newline characters. Attackers can inject malicious newline characters into names communicated over the pipe-based line-oriented protocol to cause the rsync daemon to process attacker-influenced data as legitimate protocol input, corrupting uid/gid mapping logic.
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Analysis
by VulDB Data Team • 08/13/2026
The vulnerability in rsync versions prior to 3.5.0 represents a critical security flaw that exploits weaknesses in the protocol message handling mechanism, specifically within the name-converter uid/gid mapping interface. This issue stems from insufficient input validation and sanitization of user and group identifiers that are processed through a pipe-based line-oriented communication protocol. The vulnerability allows local attackers to manipulate the system by crafting malicious usernames or group names containing newline characters, which can then be exploited to inject forged protocol messages. The fundamental technical flaw occurs when the rsync daemon processes these specially crafted identifiers without proper sanitization, leading to the corruption of uid/gid mapping logic through protocol message injection attacks.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass broader system integrity compromise and potential data manipulation capabilities. Attackers can leverage this weakness to manipulate user and group identity mappings within the rsync daemon, potentially gaining unauthorized access to files and directories that should be restricted to specific users or groups. The line-oriented nature of the protocol makes it particularly susceptible to this type of injection attack since newline characters can effectively terminate legitimate protocol commands and inject malicious instructions. This vulnerability directly relates to CWE-134, which describes the use of format strings in a context that can be influenced by an attacker, and more specifically targets CWE-74, representing improper neutralization of special elements used in data queries.
The attack vector involves creating user or group names that contain newline characters within their identifiers, which are then processed through the rsync daemon's uid/gid mapping interface. When these malicious names are communicated over the pipe-based protocol, the newline injection allows attackers to effectively split legitimate protocol messages into multiple fragments, enabling them to inject additional commands that are then interpreted as valid protocol input by the daemon. This creates a scenario where attacker-controlled data can be processed as legitimate protocol commands, potentially leading to unauthorized access, privilege escalation, or data corruption. The vulnerability is particularly dangerous in environments where rsync serves as a critical file synchronization service and where user identity mapping plays a significant role in access control decisions.
Mitigation strategies for this vulnerability should focus on immediate patching of rsync installations to version 3.5.0 or later, where the input sanitization issues have been addressed. System administrators should implement additional monitoring and logging mechanisms to detect unusual patterns in uid/gid mapping operations that might indicate exploitation attempts. The recommended approach includes enforcing strict validation of user and group identifiers at all points where they are processed by the rsync daemon, particularly within the name-converter interface. Additionally, implementing network segmentation and access controls around rsync services can limit the potential impact of exploitation. From an ATT&CK perspective, this vulnerability aligns with techniques involving privilege escalation through protocol manipulation and credential access via identity spoofing. Organizations should also consider implementing automated patch management processes to ensure timely deployment of security updates across all rsync installations within their infrastructure.
The remediation process requires careful attention to the specific implementation details of the name-converter uid/gid mapping interface, as well as thorough testing of updated configurations to ensure that legitimate user and group names continue to function properly while preventing injection attacks. The vulnerability demonstrates the importance of proper input validation in protocol handling components, particularly in services that operate with elevated privileges and handle identity information. Regular security assessments should include verification that all protocol interfaces properly sanitize inputs and do not allow special characters to be interpreted as command terminators or separators, which is a fundamental requirement for maintaining the integrity of any line-oriented communication system.