CVE-2026-17248: IBM i Denial of Service Vulnerability

CVE-2026-17248 Overview

CVE-2026-17248 affects IBM i versions 7.6, 7.5, 7.4, and 7.3. The vulnerability allows a remote authenticated attacker to trigger a denial-of-service condition through improper neutralization of special elements in an operating system command [CWE-78]. IBM assigned this issue based on flaws in how the platform processes OS command input from authenticated sessions.

The weakness sits in the OS command handling path, where malformed or specially crafted input is not sanitized before execution. Successful exploitation degrades or halts availability of the affected IBM i instance without disclosing data or modifying integrity at scale.

Critical Impact
An authenticated remote attacker can crash or destabilize IBM i midrange systems that run business-critical workloads, disrupting ERP, database, and application services.

Affected Products

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

Discovery Timeline

2026-08-12 - CVE-2026-17248 published to NVD
2026-08-12 - Last updated in NVD database

Technical Details for CVE-2026-17248

Vulnerability Analysis

The flaw is classified under [CWE-78], Improper Neutralization of Special Elements used in an OS Command. IBM i accepts input that is passed into an operating system command context without sufficient sanitization of shell or command metacharacters. When an authenticated user submits crafted input, the platform mishandles those special elements and enters a failure state that disrupts availability.

Because the attack vector is network-based and requires only low privileges, any account with authenticated access to a vulnerable service path can trigger the condition. Confidentiality is not impacted, integrity impact is limited, but availability impact is high. The vulnerability affects the entire supported release train of IBM i, indicating the defect resides in a long-standing command processing component.

Root Cause

The root cause is missing or incomplete neutralization of special characters passed to an OS command interpreter within IBM i. Special elements that should be escaped, quoted, or rejected are instead forwarded into the command pipeline. This produces malformed command execution and terminates or destabilizes the handling process, resulting in denial of service.

Attack Vector

Exploitation requires network reachability to a vulnerable IBM i service and valid user credentials. The attacker submits a crafted request containing special shell or command metacharacters through a supported interface. No user interaction is required beyond the attacker's own authenticated session. Refer to the IBM Support Document for vendor-specific technical detail on affected components and interfaces.

Detection Methods for CVE-2026-17248

Indicators of Compromise

Unexpected termination or restart of IBM i subsystems, jobs, or services shortly after authenticated command input from remote sessions.
Audit journal entries (QAUDJRN) showing commands issued by low-privilege users containing shell metacharacters such as ;, |, &, backticks, or $().
Repeated failed or malformed command executions originating from a single authenticated user or IP.

Detection Strategies

Enable and monitor IBM i security audit journaling (QAUDJRN) for command-string events (*CMD audit level) and flag unusual metacharacter patterns.
Correlate authentication events with subsequent subsystem or job failures to identify DoS attempts.
Alert on repeated abnormal terminations of the same service or QSYSWRK subsystem job following remote authenticated activity.

Monitoring Recommendations

Forward IBM i audit and message queue data to a centralized SIEM for correlation across authentication, command, and availability events.
Baseline normal command usage per user role and alert on deviations, particularly commands containing shell metacharacters.
Track service uptime and job abort counts for the affected IBM i partitions and generate alerts on statistical anomalies.

How to Mitigate CVE-2026-17248

Immediate Actions Required

Apply the IBM-supplied PTFs referenced in the IBM Support Document for IBM i 7.6, 7.5, 7.4, and 7.3.
Restrict network access to IBM i management and command interfaces to trusted administrative networks only.
Review user profiles and remove or downgrade unnecessary command-line access (LMTCPB(*YES)) for non-administrative accounts.

Patch Information

IBM has published remediation guidance in the IBM Support Document. Administrators should identify the applicable Group PTF or individual PTF for each installed IBM i release (7.3, 7.4, 7.5, 7.6) and apply it during a scheduled maintenance window. Verify PTF installation with DSPPTF after applying.

Workarounds

Limit which users can issue commands by setting LMTCPB(*YES) on user profiles that do not require command-line capability.
Enforce strict authentication controls and multi-factor authentication for all remote sessions to IBM i.
Filter or block untrusted network access to IBM i services at the network perimeter until PTFs are applied.

bash

# Configuration example: restrict command-line capability for a user profile on IBM i
CHGUSRPRF USRPRF(EXAMPLEUSR) LMTCPB(*YES)

# Verify installed PTFs after remediation
DSPPTF LICPGM(5770SS1)