CVE-2026-14276: IBM i Access Client Solutions RCE Vulnerability

CVE-2026-14276 Overview

CVE-2026-14276 affects IBM i Access Client Solutions versions 1.1.2.0 through 1.1.9.15. An authenticated user can execute arbitrary commands with normal user privileges by leveraging improper input validation in the emulator macro RunProgram action. The flaw is classified under CWE-78: OS Command Injection and is exploitable over the network with low attack complexity. Successful exploitation grants command execution in the context of the authenticated user, extending an attacker's foothold on affected systems.

Critical Impact

An authenticated attacker can execute arbitrary operating system commands on hosts running vulnerable versions of IBM i Access Client Solutions through a crafted emulator macro.

Affected Products

• IBM i Access Family 1.1.2.0 through 1.1.9.15
• IBM i Access Client Solutions (ACS) emulator component
• Windows, macOS, and Linux workstations running affected ACS versions

Discovery Timeline

• 2026-09-14 - CVE-2026-14276 published to NVD
• 2026-09-17 - Last updated in NVD database

Technical Details for CVE-2026-14276

Vulnerability Analysis

IBM i Access Client Solutions provides terminal emulation for connecting to IBM i systems. The emulator supports macros containing scripted actions, including the RunProgram action, which invokes external programs from within a macro session. The vulnerability stems from insufficient validation of user-supplied input passed to this action.

An authenticated user who can load or supply a malicious emulator macro can inject command arguments or shell metacharacters. When the emulator processes the macro, it invokes RunProgram with attacker-controlled parameters and executes arbitrary commands under the current user's privileges. The scope remains unchanged, so execution is limited to the invoking user's rights rather than escalating to administrative or system context.

Root Cause

The defect is an [CWE-78] OS Command Injection weakness. The RunProgram macro action fails to sanitize or neutralize special characters within the program name or argument fields. Values sourced from a macro file flow directly into a process-launch primitive without an allow-list, quoting, or argument boundary enforcement.

Attack Vector

Exploitation requires low-privilege authentication and no user interaction beyond loading a macro that the attacker controls or has replaced. Typical delivery paths include shared network locations hosting emulator macros, macros distributed through phishing, or macros modified in a user's ACS profile directory. Once the macro executes, injected commands run in the security context of the ACS process owner. See the IBM Support Page for vendor technical details.

No public proof-of-concept exploit is available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2026-14276

Indicators of Compromise

• Unexpected child processes spawned by acslaunch_win-64.exe, acslaunch.exe, or the Java runtime executing acsbundle.jar.
• Emulator macro files (.mac) containing RunProgram directives with shell metacharacters such as &, |, ;, or backticks.
• Modifications to macros stored under user ACS profile directories from non-standard sources or accounts.

Detection Strategies

• Inspect .mac files across user profiles and shared drives for RunProgram actions referencing unusual binaries, scripts, or encoded arguments.
• Correlate ACS process launches with subsequent execution of command interpreters (cmd.exe, powershell.exe, /bin/sh) that have no legitimate business purpose.
• Baseline normal ACS usage per user and alert on new parent-child process relationships involving ACS binaries.

Monitoring Recommendations

• Enable process creation logging (Windows Event ID 4688 or Sysmon Event ID 1) on workstations running ACS.
• Forward endpoint process telemetry to a centralized analytics platform for retention and hunting.
• Monitor file integrity on macro directories and network shares that store ACS macros for unauthorized changes.

How to Mitigate CVE-2026-14276

Immediate Actions Required

• Inventory all endpoints running IBM i Access Client Solutions and identify installations at versions 1.1.2.0 through 1.1.9.15.
• Upgrade affected installations to the fixed release identified in the IBM Support advisory.
• Restrict write access to macro storage locations to trusted administrators only.
• Review existing .mac files for unauthorized RunProgram entries and remove suspicious macros.

Patch Information

IBM has published remediation guidance in the vendor advisory. Administrators should consult the IBM Support Page for node 7287166 for the exact fixed version and download links, and deploy the update across all affected workstations.

Workarounds

• Disable or remove the emulator macro functionality where it is not required by users.
• Enforce application allow-listing to block execution of unexpected child processes from ACS binaries.
• Store macros in read-only locations governed by change control and signed distribution.
• Apply least-privilege principles so that ACS runs under user accounts without local administrator rights.

# Example: enumerate ACS macro files for review on Windows
dir /S /B "%APPDATA%\IBM\iAccessClient\Emulator\*.mac"

# Example: search macros for RunProgram actions containing shell metacharacters
findstr /S /I /C:"RunProgram" "%APPDATA%\IBM\iAccessClient\Emulator\*.mac"