CVE-2026-18069: IBM i TOCTOU Race Condition Vulnerability

CVE-2026-18069 Overview

CVE-2026-18069 is a time-of-check to time-of-use (TOCTOU) race condition affecting IBM i versions 7.6, 7.5, 7.4, and 7.3. A local attacker can exploit the flaw to obtain ownership of arbitrary file system objects on the affected system. The weakness is categorized under [CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition].

Successful exploitation lets an attacker take control of files owned by other users or system accounts. This can enable data tampering, privilege escalation, and further compromise of sensitive workloads running on IBM i.

Critical Impact
A local attacker who wins the race window can seize ownership of file system objects belonging to privileged accounts, undermining confidentiality, integrity, and availability of IBM i workloads.

Affected Products

IBM i 7.6
IBM i 7.5
IBM i 7.4
IBM i 7.3

Discovery Timeline

2026-09-14 - CVE CVE-2026-18069 published to NVD
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-18069

Vulnerability Analysis

The vulnerability stems from a race condition between the moment IBM i validates a file system object and the moment it operates on that object. During this window, an attacker with local access can substitute a different target, causing the operating system to apply a privileged action against an object the attacker does not own.

The outcome is ownership transfer of arbitrary file system objects to the attacker. Because ownership carries permission rights on IBM i, this enables the attacker to read, modify, or delete files that would otherwise be protected. The attack requires local access with low privileges, and its high attack complexity reflects the timing window that must be won.

Root Cause

The root cause is non-atomic handling of file system object references in IBM i. The code path checks properties of an object by name or path, then acts on the same reference later without ensuring the reference still points to the originally validated object. An attacker who alters the reference between the check and the use redirects the privileged operation.

Attack Vector

An authenticated local attacker triggers repeated operations that exercise the vulnerable code path. In parallel, the attacker manipulates file system paths or symbolic references so that the object validated during the check differs from the object acted upon during the use. Winning the race grants the attacker ownership of a targeted object.

No verified proof-of-concept code is publicly available. Refer to the IBM Security Advisory for vendor technical details.

Detection Methods for CVE-2026-18069

Indicators of Compromise

Unexpected changes to file system object ownership on IBM i, particularly for objects owned by QSECOFR or other privileged profiles.
Audit journal (QAUDJRN) entries showing ownership changes initiated by low-privileged user profiles.
Bursts of repeated file system operations from a single interactive or batch job, consistent with race-window brute forcing.

Detection Strategies

Enable IBM i security auditing with the *SECURITY and *OBJMGT audit values to capture object ownership changes.
Correlate CO (Create Object) and OW (Ownership Change) audit journal entries against expected administrative activity.
Alert on ownership transfers where the new owner is a non-administrative profile.

Monitoring Recommendations

Forward IBM i audit journal data to a centralized analytics platform for baseline deviation analysis.
Track process and job activity from low-privileged users that show sustained high-frequency file system syscalls.
Review scheduled and batch jobs for unauthorized modification of ownership on system libraries and IFS paths.

How to Mitigate CVE-2026-18069

Immediate Actions Required

Apply the IBM-provided PTFs referenced in the IBM Security Advisory for IBM i 7.6, 7.5, 7.4, and 7.3.
Restrict local access to IBM i systems and review user profiles with command-line and interactive access.
Enforce least privilege on user profiles and remove unnecessary *ALLOBJ or elevated special authorities.

Patch Information

IBM has published fixes for the affected releases. Consult the IBM Security Advisory for the specific PTF identifiers matching each IBM i release and apply them through standard PTF management procedures.

Workarounds

Limit interactive and SSH access to IBM i to trusted administrators until PTFs are applied.
Tighten object-level authorities on sensitive libraries and Integrated File System (IFS) directories to reduce the set of exploitable targets.
Increase audit journal review cadence to identify ownership changes quickly while patching is in progress.

bash

# Configuration example: enable auditing of object management and security events on IBM i
CHGSYSVAL SYSVAL(QAUDCTL) VALUE('*AUDLVL *OBJAUD')
CHGSYSVAL SYSVAL(QAUDLVL) VALUE('*SECURITY *OBJMGT *AUTFAIL')