CVE-2026-11378: IBM MQ DOS Vulnerability

CVE-2026-11378 is a denial of service vulnerability in IBM MQ caused by an integer overflow in distribution list processing. Authenticated attackers can exploit this to crash services or potentially execute code. This article covers technical details, affected versions, impact analysis, and mitigation strategies.

CVE-2026-11378 Overview

CVE-2026-11378 is an integer overflow vulnerability in IBM MQ that affects distribution list processing. An authenticated attacker can trigger the flaw over the network to cause denial of service or potentially execute arbitrary code on the affected queue manager. The weakness is classified as [CWE-190] Integer Overflow or Wraparound and impacts both Long Term Support (LTS) and Continuous Delivery editions of IBM MQ. IBM has published a security advisory addressing the issue.

Critical Impact
An authenticated attacker with low privileges can crash the IBM MQ queue manager or run attacker-controlled code, threatening the confidentiality, integrity, and availability of messaging infrastructure.

Affected Products

IBM MQ LTS editions (multiple versions) — see IBM advisory for exact ranges
IBM MQ Continuous Delivery editions (multiple versions)
IBM MQ 10.0.0.0 Continuous Delivery

Discovery Timeline

2026-09-18 - CVE-2026-11378 published to NVD
2026-09-23 - Last updated in NVD database

Technical Details for CVE-2026-11378

Vulnerability Analysis

The vulnerability resides in IBM MQ's handling of distribution lists, a feature that lets a single put operation deliver a message to multiple destination queues. During processing, IBM MQ performs arithmetic on values derived from the distribution list structure. When these values exceed the bounds of the destination integer type, the result wraps around and produces an incorrect size or index.

The incorrect value then flows into downstream memory allocation or copy operations. This mismatch between the allocated buffer size and the actual data length leads to memory corruption on the queue manager process. Depending on the surrounding heap state, the outcome ranges from a queue manager crash to controlled memory corruption suitable for code execution.

Exploitation requires authenticated access to the queue manager, but any low-privileged principal capable of sending messages through a distribution list can attempt the attack. Successful code execution runs in the security context of the MQ queue manager, which typically has broad access to messaging data and local resources.

Root Cause

The root cause is an unchecked arithmetic operation on attacker-influenced values during distribution list handling. Missing bounds validation allows an integer overflow that propagates into memory management logic, violating buffer size invariants.

Attack Vector

The attack vector is network-based. An authenticated MQ client submits a crafted distribution list to a vulnerable queue manager. No user interaction is required, and exploitation complexity is low. Refer to the IBM Security Advisory for CVE-2026-11378 for protocol-level details.

Detection Methods for CVE-2026-11378

Indicators of Compromise

Unexpected queue manager (amqzxma0, amqzmuc0, runmqlsr) crashes or FDC (First Failure Data Capture) files referencing distribution list processing.
Authenticated MQ sessions from unusual client hosts submitting messages with abnormally large distribution list counts.
Restart loops of MQ services correlated with a specific client channel or user identifier.

Detection Strategies

Monitor MQ error logs (AMQERR01.LOG) and FDC directories for segmentation faults or heap corruption events tied to MQPUT operations.
Baseline typical distribution list sizes per application and alert on submissions that exceed expected thresholds.
Correlate authentication events on MQ channels with subsequent queue manager instability.

Monitoring Recommendations

Forward MQ diagnostic logs and channel authentication records into a centralized analytics platform for cross-host correlation.
Track queue manager process restarts and unclean shutdowns as security-relevant events, not just availability events.
Review MQ channel authentication records (CHLAUTH) for newly created or modified low-privilege accounts.

How to Mitigate CVE-2026-11378

Immediate Actions Required

Apply the IBM MQ security update referenced in the IBM Support advisory to all LTS and Continuous Delivery deployments.
Inventory every queue manager, including containerized and appliance-based instances, and confirm each is on a fixed level.
Rotate credentials for MQ users and channels that could reach vulnerable queue managers prior to patching.

Patch Information

IBM has released fixes for the affected LTS and Continuous Delivery streams of IBM MQ. Consult the IBM Support page for this advisory for the exact fix pack, iFix identifiers, and version-to-fix mapping applicable to your deployment.

Workarounds

Restrict MQ channel access using CHLAUTH rules so only trusted client hosts and user IDs can connect to queue managers.
Disable or block use of distribution lists for applications that do not require them until patches are applied.
Enforce least privilege on MQ user accounts and remove unused authentications on remote channels.

bash

# Example CHLAUTH rule to restrict a client channel to a known host
# Run under runmqsc against the affected queue manager
SET CHLAUTH('APP.SVRCONN') TYPE(ADDRESSMAP) ADDRESS('10.10.20.15') USERSRC(CHANNEL) ACTION(REPLACE)
SET CHLAUTH('APP.SVRCONN') TYPE(BLOCKUSER) USERLIST('*MQADMIN') ACTION(REPLACE)