CVE-2026-40046 Apache Software Foundation CVE debrief

Who should care

Defenders and administrators of Apache ActiveMQ deployments should assess exposure and upgrade to fixed versions to prevent potential crashes or code execution. They should review affected scope, severity, and vendor guidance. Vulnerability management and security teams need to prioritize remediation for versions 6.0.0 to 6.2.3. Platform operators should verify and apply patches or updates according to vendor guidance.

Why it matters

CVE-2026-40046 is a high-severity vulnerability in Apache ActiveMQ that requires immediate attention from defenders and administrators. The issue arises from an incomplete fix for a previous vulnerability and affects versions 6.0.0 to 6.2.3. Upgrading to version 6.2.4 or a 5.19.x version starting with 5.19.2 or later is recommended to prevent potential crashes or code execution.

• Potential crashes or code execution due to integer overflow or wraparound
• Exposure of affected deployments to potential attacks
• Verification of upgrade to fixed versions required
• Remediation priority for versions 6.0.0 to 6.2.3

Technical summary

The vulnerability is caused by an incomplete fix for CVE-2025-66168 in Apache ActiveMQ versions 6.0.0 and later. An integer overflow or wraparound occurs due to improper validation of the MQTT control packet remaining length field. This issue affects Apache ActiveMQ, Apache ActiveMQ All, and Apache ActiveMQ MQTT versions from 6.0.0 before 6.2.4. The fix involves upgrading to version 6.2.4 or a 5.19.x version starting with 5.19.2 or later to prevent potential crashes or code execution. Defenders should assess exposure and upgrade to fixed versions.

Defensive priority

Upgrade to fixed versions to prevent potential crashes or code execution

Recommended defensive actions

• Upgrade Apache ActiveMQ to version 6.2.4
• Apply patches for 5.19.x versions starting with 5.19.2 or later
• Review and update affected deployments
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The CVE record and NVD entry provide details on the vulnerability and affected versions. Apache ActiveMQ has released security advisories and patches for the issue. Defenders should verify affected deployments, review official advisories, and plan updates or mitigations. Compensating controls should be reviewed for exposed systems while remediation is scheduled and verified. Monitoring, detection, and logs should be checked for exposed assets that need extra review.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.