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CVE-2026-12611 – Denial of Service (Unresponsive Server) – Eclipse Jetty 9.4.x, 10.0.x, 11.0.x, 12.0

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Summary

CVE-2026-12611 is a race condition in Eclipse Jetty’s HTTP/2 implementation that allows a remote, unauthenticated attacker to cause a denial of service. By sending specially timed RST_STREAM and GOAWAY frames, an attacker can cause blocking writes on the server to never unblock, eventually stalling all worker threads and making the server unresponsive. The vulnerability has a CVSS v3.1-equivalent severity of 8.7 (High) and affects a wide range of Jetty 9.4.x through 12.1.x releases.

Technical details

  • Root cause: A race condition in HTTP2Flusher allows the terminated field to be reset from a non-null value back to null while frames are being processed.
  • Trigger conditions: An attacker sends HTTP/2 RST_STREAM and GOAWAY frames to the server in a timing sequence that races with the flusher’s termination logic.
  • Attack vector: Network-based, requires no authentication and no user interaction; only HTTP/2 connectivity to the server is needed.
  • Impact: Enqueued flusher entries never complete processing, causing blocking writes to hang indefinitely. As more connections trigger the race, all available server threads become blocked, resulting in full denial of service for the affected Jetty instance.

Affected software

  • Eclipse Jetty 12.1.0 through 12.1.10
  • Eclipse Jetty 12.0.0 through 12.0.37
  • Eclipse Jetty 11.0.0 through 11.0.31
  • Eclipse Jetty 10.0.0 through 10.0.31
  • Eclipse Jetty 9.4.36 through 9.4.63

Severity

  • CVSS Score: 8.7 (High)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
  • CWE-400: Uncontrolled Resource Consumption

Mitigation and recommended actions

  • Immediate: Upgrade to a fixed Eclipse Jetty release beyond the affected version ranges listed above (i.e., a patched build past 12.1.10, 12.0.37, 11.0.31, 10.0.31, or 9.4.63) as published in the vendor’s security advisory.
  • If no patch can be applied immediately: Restrict or monitor HTTP/2 traffic to affected servers, place a reverse proxy or load balancer capable of detecting abnormal RST_STREAM/GOAWAY frame patterns in front of Jetty instances, and monitor for thread pool exhaustion or unresponsive server behavior as an indicator of exploitation attempts.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Server response header: Jetty

References

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Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

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Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

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Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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