Rsync <=3.4.3 TOCTOU Race Allows Arbitrary File Write/Privilege Escalation
CVE-2026-29518 Published on May 20, 2026
Rsync < 3.4.3 TOCTOU Race Condition Allows Symlink-Based Arbitrary File Write
Rsync versions before 3.4.3 contain a time-of-check to time-of-use (TOCTOU) race condition in daemon file handling that allows attackers to redirect file writes outside intended directories by replacing parent directory components with symbolic links. Attackers with write access to a module path can exploit this race condition to create or overwrite arbitrary files, potentially modifying sensitive system files and achieving privilege escalation when the daemon runs with elevated privileges. This vulnerability can only be triggered if the chroot setting is false.
Vulnerability Analysis
CVE-2026-29518 is exploitable with local system access, and requires small amount of user privileges. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Type
What is a TOCTTOU Vulnerability?
The software checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. This can cause the software to perform invalid actions when the resource is in an unexpected state. This weakness can be security-relevant when an attacker can influence the state of the resource between check and use. This can happen with shared resources such as files, memory, or even variables in multithreaded programs.
CVE-2026-29518 has been classified to as a TOCTTOU vulnerability or weakness.
Products Associated with CVE-2026-29518
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Affected Versions
RsyncProject rsync:- Before 3.4.3 is affected.