CVE-2026-18515 in IBM
Summary
by MITRE • 09/14/2026
IBM i 7.6, 7.5, 7.4, and 7.3 could allow a remote authenticated attacker to place files into the file system with Navigator for i when they should be blocked by Navigator configuration. This could allow attackers to upload files onto the system to places the Navigator support did not intend, but only if the profile could already do that by itself.
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Analysis
by VulDB Data Team • 09/14/2026
The vulnerability identified in IBM i versions 7.3 through 7.6 represents a logic flaw within the Navigator for i web-based management interface rather than a traditional buffer overflow or injection attack. This component serves as a graphical user interface allowing administrators to manage system resources, including file systems, remotely via standard HTTP protocols. The core issue stems from an insufficient validation mechanism when processing file placement requests initiated through this interface. Specifically, the application fails to strictly enforce configuration constraints that are designed to restrict where files can be written or moved within the operating system's hierarchical structure. This discrepancy allows a remote authenticated attacker who has valid credentials for Navigator for i to bypass intended directory restrictions and place files in locations outside of the permitted scope defined by the current security profile settings.
From a technical perspective, this flaw aligns with CWE-20 Improper Input Validation, as the system accepts input that violates its own configured policies without raising an appropriate error or rejecting the request. The attacker does not need to exploit a code execution vulnerability in the traditional sense; instead, they leverage their existing authentication privileges to manipulate file operations through the web interface. By crafting specific requests that target the underlying file handling routines of Navigator for i, the user can direct files to directories that are typically protected or restricted by system configuration. This behavior indicates a failure in the application layer's security controls, where the enforcement logic is either missing or incorrectly implemented relative to the operating system's native permission model.
The operational impact of this vulnerability is contingent upon the privileges held by the authenticated user account. As noted in the original description, the attack is only feasible if the profile already possesses the inherent ability to write files to those specific locations at an OS level. Therefore, while the Navigator for i interface does not grant new permissions that do not exist within the underlying IBM i security model, it provides a convenient and potentially less monitored vector for executing these actions remotely. An attacker with access could use this flaw to upload malicious scripts, configuration tampering files, or other payloads into sensitive directories without triggering standard file system alerts associated with direct command-line operations. This can facilitate further lateral movement or persistence within the environment if those uploaded files are subsequently executed by higher-privileged processes or services that monitor specific paths for updates or configurations.
In terms of threat modeling and industry standards, this vulnerability maps to MITRE ATT&CK technique T1505.003 Server Software Component: Web Shell, as it enables the placement of potentially malicious code into server-side directories. It also relates to T1222 File and Directory Permissions Modification if the uploaded files are used to alter access controls for subsequent exploitation attempts. The risk is amplified in environments where Navigator for i is exposed to untrusted networks or when user accounts have broad file system write permissions, as it reduces the friction required for an attacker to establish a foothold on the server.
Mitigation strategies should focus on both technical configuration and administrative oversight. IBM has released patches that address this logic flaw by enforcing stricter validation of directory paths during file operations within Navigator for i. Organizations running affected versions must apply these updates immediately to close the bypass mechanism. Additionally, administrators should review access controls for Navigator for i, ensuring that only essential personnel have authenticated access to the interface and that their assigned profiles adhere to the principle of least privilege. Restricting network exposure by placing Navigator for i behind a firewall or VPN can further reduce the attack surface. Regular auditing of file system changes in critical directories is also recommended to detect any unauthorized file placements resulting from this vulnerability before they lead to more severe compromise scenarios.