CVE-2026-53796 in rsync
Summary
by MITRE • 08/13/2026
rsync before 3.5.0 contains a time-of-check to time-of-use (TOCTOU) race condition vulnerability in the non-daemon receiver's destination directory handling that allows an attacker who can manipulate destination path parent components to redirect file writes to unintended locations. Attackers can substitute a symlink for a component of the destination path between the path resolution and chdir() call, causing the receiver's working directory to be established outside the intended destination tree so that subsequent relative-path file writes land in unintended filesystem locations.
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Analysis
by VulDB Data Team • 08/13/2026
This vulnerability represents a critical time-of-check to time-of-use race condition affecting rsync versions prior to 3.5.0, specifically within the non-daemon receiver's destination directory handling mechanism. The flaw occurs when an attacker can manipulate parent components of the destination path, creating a window where the system checks file permissions and path existence at one moment but executes file operations at a subsequent moment. This temporal discrepancy allows malicious actors to exploit the system by substituting symbolic links for legitimate directory components between the path resolution phase and the chdir() system call execution.
The technical implementation of this vulnerability stems from improper handling of directory traversal operations within rsync's receiver logic. When processing destination paths, the software performs initial path validation and checks before establishing the working directory through chdir() calls. During this interval, an attacker with control over the parent path components can create or modify symbolic links that redirect the actual file creation location. This race condition specifically impacts the non-daemon receiver functionality where rsync operates in client-server mode without running as a persistent daemon process.
The operational impact of this vulnerability extends beyond simple privilege escalation scenarios to encompass arbitrary file write operations within unintended filesystem locations. Attackers can leverage this flaw to place malicious files in system directories, modify critical configuration files, or redirect log data to locations where they can be accessed or manipulated. The vulnerability's severity is amplified because it affects the core file synchronization functionality that many systems rely upon for backup operations, file distribution, and system management tasks.
From a cybersecurity perspective, this vulnerability maps directly to CWE-367 Time-of-Check to Time-of-Use Race Condition and aligns with several ATT&CK techniques including T1059 Command and Scripting Interpreter for execution of malicious code, T1566 Phishing for Information through social engineering attacks that might exploit the vulnerability, and T1486 Data Encrypted for Data Destruction. The flaw also connects to T1078 Valid Accounts through potential privilege escalation scenarios where attackers could gain unauthorized access to sensitive system locations.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The most direct solution involves upgrading to rsync version 3.5.0 or later, which includes fixes that eliminate the race condition by ensuring consistent path resolution throughout the entire file operation sequence. Organizations should also implement strict file system permissions and access controls, particularly around directory components that may be manipulated during synchronization operations. Additional defensive measures include monitoring for suspicious symbolic link creation patterns, implementing automated scanning for compromised destination directories, and establishing robust input validation procedures for all path-related operations within rsync configurations.
The vulnerability demonstrates the importance of proper race condition handling in system utilities that process file operations with elevated privileges. It highlights how seemingly simple path resolution operations can introduce significant security risks when not properly synchronized across multiple system calls. Security teams should conduct comprehensive audits of their rsync implementations, particularly focusing on environments where untrusted users might have influence over destination paths or directory structures. Regular vulnerability assessments and penetration testing should include evaluation of similar race condition patterns in other file system utilities and network services to prevent analogous security issues from manifesting in different components of the system infrastructure.