CVE-2026-15565 Red Hat CVE debrief

Who should care

Defenders responsible for Undertow-based applications, especially those using websockets, should assess their exposure and potential impact of Denial of Service attacks. This includes operators, platform administrators, and security teams that manage and maintain Undertow-based applications. They should verify exposure, assess potential impact, and review and apply Red Hat errata for affected products.

Why it matters

CVE-2026-15565 is a high-severity vulnerability in Undertow that allows remote attackers to cause Denial of Service attacks without authentication. Defenders should prioritize verifying exposure and assessing potential impact.

• Potential Denial of Service attacks via websockets
• Need to verify exposure of Undertow-based applications
• Requirement to assess impact on business operations
• Necessity to review and apply Red Hat errata for affected products

Technical summary

The vulnerability, CVE-2026-15565, is caused by a flaw in Undertow that allows a remote attacker to cause an Out of Memory condition on websockets endpoints without authentication. This leads to a Denial of Service attack. The issue affects Red Hat JBoss Enterprise Application Platform 7.4.25. The vulnerability has a high severity score and requires immediate attention from defenders. The technical details of the vulnerability indicate that it is a critical issue that needs to be addressed promptly. The flaw in Undertow allows an attacker to cause an Out of Memory condition, which can lead to a Denial of Service attack.

Defensive priority

Defenders should prioritize verifying exposure of Undertow-based applications, especially those using websockets, and assess the impact of potential Denial of Service attacks.

Recommended defensive actions

• Verify exposure of Undertow-based applications using websockets
• Assess potential impact of Denial of Service attacks
• Review and apply Red Hat errata for affected products
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed

Evidence notes

The CVE record and NVD detail page provide information on the vulnerability, while Red Hat references offer insights into affected products and potential mitigations. The vulnerability has been reported to affect Red Hat JBoss Enterprise Application Platform 7.4.25. Defenders should verify exposure and assess potential impact. Evidence is limited, and further verification is required.

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.