CVE-2026-108140 in Backup and Replication
Summary
by MITRE • 10/27/2026
A vulnerability allowing an authenticated user with the Restore Operator role, who also controls the contents of a backed-up NAS share, to write attacker-controlled files to an arbitrary path on the backup server through relative path traversal.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability represents a critical security flaw within the backup infrastructure's restore mechanism, specifically affecting systems that utilize Network Attached Storage shares for data preservation and recovery operations. This issue is classified as a Path Traversal or Directory Traversal vulnerability, which falls under the Common Weakness Enumeration category CWE-22: Improper Limitation of a Pathname to a Restricted Directory. The core technical flaw lies in the insufficient validation of file paths during the restoration process. When an authenticated user possessing the Restore Operator role initiates a restore operation from a controlled NAS share, the application fails to adequately sanitize or canonicalize relative path references provided by the attacker. Instead of restricting the output destination strictly within the designated backup recovery directory, the system processes these relative paths without proper boundary checks, allowing them to escape the intended sandboxed environment and resolve to arbitrary locations on the underlying operating system's file hierarchy.
The operational impact of this vulnerability is severe due to the combination of authentication requirements and specific role privileges. While an attacker must first authenticate with valid credentials holding the Restore Operator role, this access level is often granted to administrative or backup management personnel who are trusted to manage data integrity. By controlling the contents of a backed-up NAS share, which could be achieved through compromising another system on the network that backs up to this storage or by manipulating shared resources if permissions allow, an attacker can craft malicious restore requests containing relative path sequences such as dot-dot-slash patterns. These sequences enable the traversal up the directory tree from the restricted backup folder into higher-level directories. Consequently, the attacker gains the ability to write arbitrary files to any location on the server where the application has file system write permissions. This capability effectively bypasses standard access controls and isolation mechanisms designed to contain restore operations within safe boundaries.
This vulnerability facilitates a wide range of malicious activities beyond simple unauthorized data placement. An attacker could overwrite critical configuration files, inject web shells or backdoors into executable directories, or corrupt essential system binaries, leading to full remote code execution on the backup server. The compromise of a backup server is particularly dangerous because it often contains sensitive historical data and may have elevated privileges for interacting with other network services. If an attacker establishes persistence by placing malicious scripts in startup directories or modifying environment variables, they can maintain access even after initial detection efforts. Furthermore, since the vulnerability relies on relative path traversal, it exploits a common programming oversight where developers assume that input from trusted sources like internal NAS shares does not require rigorous sanitization, ignoring the possibility of manipulation within those shared resources.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary technical fix involves implementing strict canonicalization of all file paths before processing restore operations. Developers should resolve relative paths to absolute paths and verify that the resulting path resides strictly within the allowed backup directory, rejecting any request where the resolved path differs from or escapes this boundary. Input validation must be applied at multiple layers, including application logic and web server configurations, ensuring that special characters and sequence patterns indicative of traversal are blocked or neutralized. Additionally, enforcing principle of least privilege is crucial; the Restore Operator role should not inherently possess write access to arbitrary system paths but rather only within a tightly controlled sandboxed environment. Regular security audits focusing on file handling routines in backup software can help identify similar weaknesses before they are exploited. Monitoring for unusual file creation patterns outside expected directories and implementing robust logging of restore operations will also aid in early detection and response to potential exploitation attempts aligned with ATT&CK techniques related to persistence and privilege escalation via local file manipulation.