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CVE-2026-19203 – HTTP Request Smuggling – Eclipse Jetty (9.4.x, 10.0.x, 11.0.x, 12.0.x, 12.1.x)

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Summary

CVE-2026-19203 is an HTTP request smuggling vulnerability (CWE-444: Inconsistent Interpretation of HTTP Requests) affecting the Eclipse Jetty web server’s HTTP/1.1 chunked transfer-encoding parser. A remote, unauthenticated client can send specially crafted chunked requests that Jetty and a front-end proxy or load balancer interpret differently, causing request boundary confusion. The issue carries a CVSS score of 8.3 (High) and affects multiple actively deployed Jetty version lines.

Technical details

  • Root cause: Jetty’s chunked request parser accepts a lone LF (line feed) character as a valid terminator in place of the required CRLF sequence, depending on the version and configured HttpCompliance mode.
  • Trigger conditions: The lenient LF handling can occur in chunk extensions, chunk data termination, or trailer termination when parsing HTTP/1.1 chunked request bodies.
  • Attack vector: Network-based; requires an intermediary (reverse proxy, load balancer, CDN) in front of Jetty that parses the same chunked request differently than Jetty does, enabling a desync between the two.
  • Impact: Successful exploitation can lead to HTTP request smuggling, allowing an attacker to have requests misinterpreted, potentially bypassing security controls, poisoning caches, or accessing content/responses intended for other users.

Affected software

  • Eclipse Jetty 12.1.0 – 12.1.11
  • Eclipse Jetty 12.0.0 – 12.0.37
  • Eclipse Jetty 11.0.0 – 11.0.31
  • Eclipse Jetty 10.0.0 – 10.0.31
  • Eclipse Jetty 9.4.0 – 9.4.63

Severity

  • CVSS v4.0 Base Score: 8.3 (High)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:H/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade to Jetty 12.0.38 or 12.1.12, both of which remove lone-LF chunk termination from non-legacy HttpCompliance modes and resolve this issue.
  • If no patch available: Jetty 9.4, 10.0, and 11.0 reached end of community support and, as of January 1, 2026, no further public releases are being published for these lines — organizations on these versions will not receive an official fix and should prioritize migrating to a supported Jetty 12.x release. As an interim mitigation, ensure any front-end proxy/load balancer enforces strict RFC-compliant chunked encoding parsing (rejecting lone-LF terminators) so it cannot be desynchronized from Jetty’s interpretation of request boundaries.

How IONIX identifies potentially affected assets

IONIX matches the following signal 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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