CVE-2026-19204 Eclipse Foundation CVE debrief

Who should care

Defenders responsible for systems using Jetty with WebSocket and auto-fragmentation enabled should assess exposure and potential impact. This includes operators, platform administrators, vulnerability management teams, and security teams who need to verify Jetty version and configuration, and monitor for unusual activity.

Why it matters

CVE-2026-19204 is a high-severity vulnerability in Jetty's WebSocket implementation that could lead to denial-of-service (DoS) through memory exhaustion. Defenders responsible for systems using Jetty with WebSocket and auto-fragmentation enabled should assess exposure and potential impact, and verify Jetty version and configuration.

• Potential for denial-of-service (DoS) through memory exhaustion
• Need for verification of Jetty version and configuration
• Possible impact on system availability and performance

Technical summary

CVE-2026-19204 is a high-severity vulnerability in Jetty's WebSocket implementation. A client can send a WebSocket frame with an unknown opcode and a large declared payload length, potentially causing a large memory allocation and exhausting the JVM heap when auto-fragmentation is enabled. This occurs because unknown opcodes bypass normal maximum frame size handling, and payload allocation occurs before opcode validation.

Defensive priority

Defenders should prioritize verifying exposure and assessing potential impact, focusing on systems using Jetty with WebSocket and auto-fragmentation enabled.

Recommended defensive actions

• Verify Jetty version and configuration
• Assess exposure and potential impact
• Monitor for unusual WebSocket activity
• Review compensating controls for exposed systems
• Check relevant monitoring, detection, and logs for exposed assets
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, but additional information on affected versions, exploitation, and remediation is limited. Defenders should verify Jetty version and configuration, assess exposure, and monitor for unusual WebSocket activity. The CVE Program record and NVD detail page offer source-provided CVE metadata and vulnerability assessments.

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.