CVE-2026-18515 Overview
CVE-2026-18515 affects IBM i versions 7.6, 7.5, 7.4, and 7.3. A remote authenticated attacker can place files into the file system using Navigator for i when Navigator configuration should block the action. The flaw allows attackers to upload files to locations the Navigator support did not intend to permit. Exploitation only succeeds when the user profile already possesses the underlying authority to write to those locations. IBM classifies this as a path traversal weakness [CWE-22].
Critical Impact
Authenticated users can bypass Navigator for i upload restrictions and place files outside intended directories, undermining administrative controls on file placement.
Affected Products
- IBM i 7.6
- IBM i 7.5
- IBM i 7.4
- IBM i 7.3
Discovery Timeline
- 2026-09-14 - CVE-2026-18515 published to NVD
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-18515
Vulnerability Analysis
Navigator for i provides a web-based administration interface for the IBM i operating system. The interface enforces configuration-based restrictions on where authenticated users can upload files through the Navigator UI. This vulnerability breaks that enforcement layer. An authenticated attacker can bypass the Navigator upload restrictions and place files in filesystem locations that the Navigator configuration was intended to block.
The issue does not grant new operating system privileges. The attacker must already hold a user profile with sufficient IBM i authority to write to the target directory. The vulnerability removes the Navigator-layer control that would otherwise prevent the profile from staging files there through the Navigator interface. This weakens defense-in-depth and enables misuse where administrators relied on Navigator configuration as the enforcement point.
Root Cause
The root cause is improper limitation of a pathname to a restricted directory [CWE-22] within Navigator for i. Navigator does not correctly validate or normalize target upload paths against its configured restriction policy. Path components processed by the upload handler allow the resolved destination to escape the intended boundary.
Attack Vector
Exploitation requires network access to Navigator for i and valid authenticated credentials. An attacker submits an upload request through Navigator with a crafted target path that resolves outside the configured allowed locations. Navigator writes the file using the authority of the caller's profile. If that profile has native filesystem authority to the resolved destination, the write succeeds despite the Navigator restriction.
No verified public proof-of-concept exists. Refer to the IBM Support Page for vendor technical details.
Detection Methods for CVE-2026-18515
Indicators of Compromise
- Files appearing in IFS directories that Navigator for i policy was configured to block
- Navigator for i HTTP request logs containing upload operations with path traversal sequences such as ../ or encoded variants
- Unexpected file writes performed by the Navigator server job under a low-privilege user profile
Detection Strategies
- Correlate Navigator for i web server access logs against IFS file creation events to identify writes outside approved upload directories
- Audit IBM i journal receivers (QAUDJRN) for object creation entries (type CO) originating from Navigator processes
- Baseline permitted upload paths per profile and alert on writes outside that baseline
Monitoring Recommendations
- Enable IBM i security auditing for object creation and access events across sensitive IFS paths
- Forward Navigator for i and QAUDJRN telemetry to a centralized SIEM for retention and correlation
- Review authenticated Navigator sessions for unusual upload volume or destinations outside expected administrative use
How to Mitigate CVE-2026-18515
Immediate Actions Required
- Apply the IBM-provided fix for Navigator for i on all affected releases (7.6, 7.5, 7.4, 7.3) as documented on the IBM Support Page
- Review IBM i user profile authorities and remove write access to sensitive IFS directories from profiles that do not require it
- Audit recent Navigator for i uploads for files placed outside intended locations
Patch Information
IBM has published remediation guidance and fix availability on the IBM Support Page for CVE-2026-18515. Administrators should identify the applicable PTF for each installed IBM i release and apply it during the next maintenance window.
Workarounds
- Restrict network access to Navigator for i to trusted administrative subnets until patches are applied
- Reduce the authority of Navigator user profiles so filesystem authority alone blocks unauthorized writes
- Disable Navigator for i features that are not required in the environment to reduce exposed upload endpoints
# Example: restrict IFS authority to limit impact of the Navigator bypass
CHGAUT OBJ('/sensitive/path') USER(SUSPECT_PROFILE) DTAAUT(*EXCLUDE) OBJAUT(*NONE)
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
