CVE-2026-18073: IBM i Privilege Escalation Vulnerability

CVE-2026-18073 Overview

CVE-2026-18073 is a parameter injection vulnerability in IBM i versions 7.3, 7.4, 7.5, and 7.6. The flaw stems from improper neutralization of special elements when constructing Control Language (CL) commands. A local authenticated attacker can inject additional parameters into a CL command, altering its intended behavior. IBM classifies this issue under CWE-78: Improper Neutralization of Special Elements used in an OS Command. The vulnerability requires local access with existing privileges, limiting its exposure to insider or post-compromise scenarios.

Critical Impact
Successful exploitation allows a local authenticated user to manipulate CL command execution, leading to limited confidentiality and integrity impact on affected IBM i systems.

Affected Products

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

Discovery Timeline

2026-09-04 - CVE-2026-18073 published to NVD
2026-09-08 - Last updated in NVD database

Technical Details for CVE-2026-18073

Vulnerability Analysis

The vulnerability resides in how IBM i processes CL command strings that incorporate user-controllable input. IBM i uses Control Language as its primary scripting and administration interface. When special characters within input are not properly neutralized, an attacker can append or modify command parameters. This changes the operational context of the command being executed. The result is unauthorized data access or modification within the scope of the invoking process.

The issue aligns with CWE-78, which covers OS command injection through improper input sanitization. Because the attack vector is local and requires low privileges, the impact is limited to what the authenticated user context permits. Confidentiality and integrity are partially affected, while availability is not impacted.

Root Cause

The root cause is insufficient neutralization of special characters and delimiters passed to CL command processors. Input that should be treated as data is instead interpreted as additional command syntax. This creates a boundary violation between control and data planes within the command interpreter.

Attack Vector

Exploitation requires local access to the IBM i system and valid authenticated credentials. The attacker supplies crafted input to an interface or application that constructs CL commands. By embedding delimiter or metacharacter sequences, the attacker injects unintended parameters. No user interaction beyond the attacker's own session is required. Refer to the IBM Support advisory for vendor-provided technical detail.

Detection Methods for CVE-2026-18073

Indicators of Compromise

Unexpected CL command invocations in QHST or job logs containing unusual parameter sequences or delimiters.
Audit journal (QAUDJRN) entries showing command execution by users outside their normal operational scope.
Anomalous CHGCMD, CALL, or SBMJOB activity originating from application service profiles.

Detection Strategies

Enable and review QAUDJRN with *CMD auditing to capture command strings executed across the system.
Baseline expected CL command patterns per application and alert on deviations, particularly extra parameters or embedded quotes.
Correlate command execution events with user profile activity to identify privilege boundary violations.

Monitoring Recommendations

Forward IBM i audit journal data to a centralized SIEM for retention and correlation across hosts.
Monitor application interfaces that accept user input and pass values to CL commands for parameter tampering attempts.
Track cumulative failed and successful command executions per user profile to identify abuse patterns.

How to Mitigate CVE-2026-18073

Immediate Actions Required

Apply the IBM-provided fixes documented in the IBM Support advisory for each affected release.
Inventory IBM i systems running versions 7.3, 7.4, 7.5, and 7.6 and prioritize those exposing user-facing CL command interfaces.
Review and restrict local user profile authorities using the principle of least privilege.

Patch Information

IBM has published remediation guidance and PTF references on the IBM Support page for CVE-2026-18073. Administrators should apply the Program Temporary Fixes (PTFs) that correspond to their installed IBM i release and cumulative level.

Workarounds

Validate and sanitize all user-supplied input before incorporating it into CL command strings within custom applications.
Use parameterized command interfaces such as QCMDEXC with explicit length arguments rather than dynamic string concatenation.
Restrict access to programs and menus that construct CL commands from external input to trusted user profiles only.

bash

# Review command auditing configuration on IBM i
DSPSYSVAL SYSVAL(QAUDCTL)
DSPSYSVAL SYSVAL(QAUDLVL)

# Enable command auditing for a specific user profile
CHGUSRAUD USRPRF(SUSPECTUSER) AUDLVL(*CMD)