CVE-2026-56816: Netty memory exhaustion in Http3FrameCodec

Executive brief

Netty, a popular networking framework for Java applications, contains a vulnerability in its HTTP/3 implementation. An attacker can send specially crafted network traffic that forces the server to consume excessive amounts of memory. This can lead to a system crash or service outage, preventing legitimate users from accessing the application.

Technical details

An uncontrolled resource consumption vulnerability exists in Netty's Http3FrameCodec. The decodeFrame method handles HTTP/3 reserved frame types by reading the payload length directly from the wire and trusting it without validation. An unauthenticated remote attacker can send a reserved frame with a payload length up to Integer.MAX_VALUE across multiple QUIC streams. This causes the server to buffer data in memory until the specified length is reached, leading to OutOfMemory (OOM) errors and a Denial of Service (DoS). The issue is fixed in version 4.2.16.Final.

Affected products

• Netty netty-codec-http3 < 4.2.16.Final

Timeline

• 2026-07-14: patched: Fix released in version 4.2.16.Final
• 2026-07-21: advisory: NVD publication date
• 2026-07-22: disclosed: GitHub Advisory published

References

• https://api.github.com/users/violetagg
• https://github.com/violetagg
• https://api.github.com/users/violetagg/gists%7B/gist_id%7D
• https://api.github.com/users/violetagg/repos
• https://avatars.githubusercontent.com/u/696661?v=4
• https://api.github.com/users/violetagg/events%7B/privacy%7D