CVE-2004-0426 in rsync
Summary
by MITRE
rsync before 2.6.1 does not properly sanitize paths when running a read/write daemon without using chroot, which allows remote attackers to write files outside of the module s path.
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Analysis
by VulDB Data Team • 07/12/2025
The vulnerability described in CVE-2004-0426 represents a critical path traversal flaw in rsync versions prior to 2.6.1 that affects the daemon mode operation when chroot is not employed. This security weakness stems from inadequate input validation and path sanitization mechanisms within the rsync daemon implementation, creating a scenario where remote attackers can manipulate file paths to write data beyond the intended module boundaries. The vulnerability specifically targets configurations where rsync operates as a daemon service without the security restriction of chroot jail, leaving the system exposed to unauthorized file system modifications. The flaw allows malicious actors to exploit the path handling logic to escape the designated module directories and potentially overwrite or create files in arbitrary locations on the target system.
The technical exploitation of this vulnerability occurs through the manipulation of file paths during rsync daemon operations, where the software fails to properly validate or sanitize path components received from remote clients. When rsync runs in daemon mode without chroot, it processes file operations relative to the module's root directory but does not adequately filter or canonicalize path references that may contain directory traversal sequences such as "../" or similar constructs. This inadequate sanitization allows attackers to craft malicious file paths that, when processed by the rsync daemon, result in unintended file system modifications outside the module's designated scope. The vulnerability operates at the application layer and can be exploited remotely, making it particularly dangerous in networked environments where rsync daemons are exposed to untrusted networks. This flaw aligns with CWE-22 Path Traversal and CWE-77 Path Traversal vulnerabilities, which are categorized under the broader weakness of improper input validation and inadequate path sanitization.
The operational impact of this vulnerability extends beyond simple unauthorized file creation, as it can potentially enable attackers to overwrite critical system files, inject malicious code, or establish persistent access points within the compromised system. Remote attackers who can connect to the rsync daemon service can leverage this weakness to escalate privileges or cause system instability by modifying files in protected directories. The vulnerability is particularly concerning because it affects the core functionality of rsync's daemon mode, which is commonly used for automated backup and synchronization operations. Attackers can exploit this issue to gain unauthorized access to system resources, potentially leading to complete system compromise. The vulnerability's impact is amplified in environments where rsync daemons are configured with weak authentication or are exposed to the internet without proper network segmentation. According to ATT&CK framework, this vulnerability maps to T1078 Valid Accounts and T1566 Phishing, as attackers can use the compromised rsync service to establish persistence or gain access to additional system resources through unauthorized file modifications.
Mitigation strategies for CVE-2004-0426 require immediate implementation of software updates to rsync version 2.6.1 or later, which contain the necessary path sanitization fixes. Organizations should also implement mandatory chroot restrictions for rsync daemon operations, ensuring that all daemon instances operate within isolated directory environments that prevent path traversal attacks. Network segmentation and firewall rules should be enforced to limit access to rsync daemon ports to trusted networks only, while proper authentication mechanisms should be implemented to prevent unauthorized connections. Additionally, system administrators should conduct regular security audits of rsync configurations to verify that chroot restrictions are properly enforced and that no vulnerable daemon instances remain operational. The vulnerability underscores the importance of proper input validation and the principle of least privilege in security implementations, particularly for services that operate with elevated system permissions. Organizations should also consider implementing intrusion detection systems to monitor for suspicious rsync daemon activities and maintain updated vulnerability management processes to ensure timely patch deployment across all affected systems.