CVE-2026-53790 in Rsync
Summary
by MITRE • 08/13/2026
rsync before 3.5.0 contains multiple command and argument injection vulnerabilities that allow attackers to execute arbitrary commands by supplying malicious input through several code paths, including the RSYNC_CONNECT_PROG environment variable, daemon hooks, the rsync-ssl wrapper, and remote-shell command newline injection. Attackers can inject shell metacharacters or newline characters into unsanitized user-supplied values such as hostnames and hostspecs to execute arbitrary commands under the privileges of the rsync process or the invoking user.
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Analysis
by VulDB Data Team • 08/13/2026
The rsync vulnerability affecting versions prior to 3.5.0 represents a critical command injection flaw that spans multiple attack vectors within the file synchronization utility. This vulnerability stems from insufficient input sanitization across various code paths, allowing attackers to inject malicious shell commands through environment variables and user-supplied parameters. The RSYNC_CONNECT_PROG environment variable serves as one primary entry point where unvalidated input can be exploited to execute arbitrary code, while daemon hooks provide another avenue for command injection attacks. The rsync-ssl wrapper functionality introduces additional risk by failing to properly sanitize inputs before processing them within shell contexts. These vulnerabilities collectively create a pathway for attackers to escalate privileges and execute malicious commands with the same permissions as the rsync process or the invoking user, making this issue particularly dangerous in environments where rsync operates with elevated privileges.
The technical implementation of these injection flaws demonstrates poor input validation practices that align with CWE-74 standards for injection vulnerabilities. The vulnerability manifests when attackers can manipulate unsanitized user-supplied values such as hostnames and hostspecs to include shell metacharacters or newline characters. This type of exploitation directly maps to ATT&CK technique T1059.001 for command and script injection, where adversaries leverage legitimate system tools to execute malicious payloads. The newline character injection specifically targets the remote-shell command execution flow, allowing attackers to append additional commands that will be executed by the underlying shell environment. The lack of proper escaping or validation in these code paths creates persistent security weaknesses that can be exploited regardless of the specific rsync invocation method used.
The operational impact of this vulnerability extends beyond simple command execution to potentially compromise entire systems where rsync is deployed with administrative privileges. Attackers exploiting these vulnerabilities can gain unauthorized access to sensitive data, modify system configurations, or establish persistence mechanisms within target environments. The scope of affected installations includes any deployment of rsync versions prior to 3.5.0 that utilize the vulnerable code paths, particularly in enterprise environments where rsync is commonly used for backup operations, file synchronization, and remote system management. Organizations running rsync as a daemon service or with elevated privileges face the highest risk exposure, as successful exploitation can lead to complete system compromise. The vulnerability's impact is further amplified when rsync is integrated into automated workflows or scheduled tasks, where attackers can leverage these injection points for persistent access.
Mitigation strategies for this vulnerability require immediate patching of rsync installations to version 3.5.0 or later, which contains the necessary input validation fixes. Organizations should also implement network segmentation and access controls to limit exposure of rsync services to trusted networks only. Input sanitization measures including proper shell escaping, parameter validation, and environment variable handling should be enforced throughout all rsync configurations. Security monitoring systems should be enhanced to detect suspicious command execution patterns or unusual rsync behavior that might indicate exploitation attempts. Additionally, system administrators should review and restrict the use of environment variables such as RSYNC_CONNECT_PROG in production environments where possible, and implement principle of least privilege when configuring rsync daemon operations. The vulnerability highlights the importance of thorough input validation in system utilities and demonstrates how seemingly benign configuration options can become security attack vectors when proper sanitization measures are absent from the codebase.