A flaw was found in Undertow. A remote attacker can cause Out of Memory on websockets endpoint without authentication on any @ServerEndpoint class… (CVE-2026-15565)
A vulnerability in Undertow allows a remote attacker to cause an Out of Memory condition on WebSocket endpoints without authentication on any @ServerEndpoint class that has an @OnMessage method. This can lead to a denial of service (DoS) attack using only a standard WebSocket handshake. The issue is tracked as CVE-2026-15565 with a CVSS score of 7.5 (high severity).
AI Analysis
Technical Summary
CVE-2026-15565 is a denial of service vulnerability in Undertow's WebSocket implementation. A remote attacker can trigger unbounded memory consumption on any @ServerEndpoint class that implements an @OnMessage method by initiating a standard WebSocket handshake, without requiring authentication. This flaw results in an Out of Memory condition, causing service disruption. The vulnerability is classified under CWE-120 (Buffer Copy without Checking Size of Input). Red Hat has published an advisory for Red Hat JBoss Enterprise Application Platform 7.4.25 addressing this issue and provides configuration-based mitigations to disable WebSocket handshakes either server-wide or per application.
Potential Impact
The vulnerability allows an unauthenticated remote attacker to cause a denial of service by exhausting memory resources on the WebSocket endpoint, leading to service unavailability. There is no impact on confidentiality or integrity, but availability is severely affected.
Mitigation Recommendations
Red Hat provides configuration-based mitigations to disable WebSocket handshakes. Option 1 is to remove the <websockets/> element from the standalone.xml servlet-container configuration to disable WebSocket support server-wide. Option 2 is to disable WebSockets per application by setting <enable-websockets>false</enable-websockets> in the WEB-INF/jboss-web.xml file inside the WAR. These mitigations prevent the registration of @ServerEndpoint classes and block WebSocket upgrade requests, effectively mitigating the vulnerability. A security update is available in Red Hat JBoss Enterprise Application Platform 7.4.25. Users should apply this update after ensuring all prior errata are applied and back up their systems accordingly. Patch status is confirmed as an official fix available from Red Hat.
A flaw was found in Undertow. A remote attacker can cause Out of Memory on websockets endpoint without authentication on any @ServerEndpoint class… (CVE-2026-15565)
Description
A vulnerability in Undertow allows a remote attacker to cause an Out of Memory condition on WebSocket endpoints without authentication on any @ServerEndpoint class that has an @OnMessage method. This can lead to a denial of service (DoS) attack using only a standard WebSocket handshake. The issue is tracked as CVE-2026-15565 with a CVSS score of 7.5 (high severity).
CVSS v3.1
Score 7.5high
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-15565 is a denial of service vulnerability in Undertow's WebSocket implementation. A remote attacker can trigger unbounded memory consumption on any @ServerEndpoint class that implements an @OnMessage method by initiating a standard WebSocket handshake, without requiring authentication. This flaw results in an Out of Memory condition, causing service disruption. The vulnerability is classified under CWE-120 (Buffer Copy without Checking Size of Input). Red Hat has published an advisory for Red Hat JBoss Enterprise Application Platform 7.4.25 addressing this issue and provides configuration-based mitigations to disable WebSocket handshakes either server-wide or per application.
Potential Impact
The vulnerability allows an unauthenticated remote attacker to cause a denial of service by exhausting memory resources on the WebSocket endpoint, leading to service unavailability. There is no impact on confidentiality or integrity, but availability is severely affected.
Mitigation Recommendations
Red Hat provides configuration-based mitigations to disable WebSocket handshakes. Option 1 is to remove the <websockets/> element from the standalone.xml servlet-container configuration to disable WebSocket support server-wide. Option 2 is to disable WebSockets per application by setting <enable-websockets>false</enable-websockets> in the WEB-INF/jboss-web.xml file inside the WAR. These mitigations prevent the registration of @ServerEndpoint classes and block WebSocket upgrade requests, effectively mitigating the vulnerability. A security update is available in Red Hat JBoss Enterprise Application Platform 7.4.25. Users should apply this update after ensuring all prior errata are applied and back up their systems accordingly. Patch status is confirmed as an official fix available from Red Hat.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-356w-cx4r-75hv
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-15565"]
- Ecosystems
- []
- Database Specific Severity
- HIGH
- Cvss Version
- 3.1
Patch Information
Threat ID: 6a7cd3f2bf8831d539180a53
Added to database: 08/12/2026, 20:13:38 UTC
Last enriched: 08/12/2026, 20:26:53 UTC
Last updated: 08/13/2026, 02:40:59 UTC
Views: 4
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