CVE-2026-53784 in Rsync
Summary
by MITRE • 08/13/2026
rsync before 3.5.0 contains a path traversal vulnerability that allows remote clients to access files outside the intended module root when use chroot is disabled and the module root path or a component of it is a symlink. The daemon calls chdir() to the module root at session initialization without resolving symlinks via realpath() or equivalent, causing subsequent relative-path operations to reference files relative to the symlink target rather than the intended module root, enabling unauthorized file access.
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Analysis
by VulDB Data Team • 08/13/2026
This vulnerability represents a critical path traversal flaw in rsync versions prior to 3.5.0 that fundamentally undermines the security boundaries of the file synchronization daemon. The issue arises from improper handling of symbolic links within the module root configuration, creating an unexpected attack vector that bypasses intended access controls. When rsync operates without chroot enabled and encounters a symlinked module root path, the daemon fails to canonicalize the path through proper resolution mechanisms such as realpath() or equivalent functions.
The technical implementation of this vulnerability stems from how rsync initializes session directories during daemon startup. At this critical point in execution, the system performs a simple chdir() operation to the configured module root without first normalizing the path to eliminate symbolic link references. This design flaw allows attackers to manipulate the path traversal through carefully crafted relative paths that exploit the symlink resolution behavior. The vulnerability specifically manifests when a module root directory is itself a symbolic link pointing to an arbitrary location outside the intended scope, creating a scenario where subsequent file operations reference locations different from what the administrator intended to protect.
The operational impact of this vulnerability extends beyond simple unauthorized file access to encompass potential data exfiltration and system compromise scenarios. An attacker with remote access to the rsync daemon can leverage this flaw to read files from any location accessible to the rsync process, potentially including sensitive system files, configuration data, or user documents that should remain protected within the intended module boundaries. The vulnerability affects systems where rsync is configured with chroot disabled, which is common in many deployment scenarios where administrators rely on other security mechanisms for access control.
This specific flaw maps directly to CWE-22 Path Traversal and aligns with ATT&CK technique T1078 Valid Accounts for maintaining persistent access while leveraging legitimate system functionality. The vulnerability demonstrates how seemingly benign path handling operations can create significant security implications when symbolic link resolution is not properly managed. Organizations implementing rsync services without chroot protection face heightened risk of data exposure, particularly in environments where multiple users or services share the same daemon instance. The attack vector requires minimal privileges and can be executed remotely, making it particularly dangerous for publicly accessible rsync installations.
Mitigation strategies should prioritize immediate patching to rsync version 3.5.0 or later, which implements proper symlink resolution during module root initialization. Organizations should also consider enabling chroot functionality where possible, as this provides an additional layer of protection even if the underlying vulnerability exists. Security configurations should avoid using symbolic links in module root paths when chroot is disabled, and administrators should implement strict access controls limiting rsync daemon exposure to trusted networks only. Regular security auditing of rsync configurations can help identify potential symlink-based vulnerabilities before they can be exploited by malicious actors.