CVE-2026-50560: Netty susceptible to HTTP/2 Reset Attack with different on-the-wire signature
Summary
Netty HTTP/2 max header size handling produces attack similar to HTTP/2 Rapid Reset.
Details
There is a setting in the http2 specification called SETTINGSMAXHEADERLISTSIZE. According to the RFC: “This advisory setting informs a peer of the maximum field section size that the sender is prepared to accept, in units of octets.”
When a client sends that setting to Netty, it appears that Netty will behave as follows:
- Read the request - Proxy the request to the origin - Attempt to produce a response - Create an exception while writing the headers for the response
Functionally, this should be similar to the http2 reset attack, but with a different on-the-wire signature.
Remediation
When speaking with clients, Netty should potentially treat this as “advisory” and ignore it. It would be best to ignore the SETTINGSMAXHEADERLISTSIZE setting from clients (or ignore it when sending to clients). According to the spec, a server does not need to honor this advisory setting, and it appears that other http/2 implementations ignore it when acting as a server.
Impact
This is a DDoS attack similar to the HTTP/2 Rapid Reset Attack.
Credit Jonathan Looney (Engineering, Netflix)
Contact Ashley Tolbert (Security, Netflix) - artolbert@netflix.com
Other sources
Netty is a network application framework for development of protocol servers and clients. Prior to versions 4.1.135.Final and 4.2.15.Final, Netty HTTP/2 max header size handling produces an attack similar to HTTP/2 Rapid Reset. There is a setting in the http2 specification called SETTINGSMAXHEADERLISTSIZE. When a client sends that setting to Netty, it appears that Netty will behave as follows: read the request; proxy the request to the origin; attempt to produce a response; and create an exception while writing the headers for the response. Functionally, this should be similar to the http2 reset attack, but with a different on-the-wire signature. Versions 4.1.135.Final and 4.2.15.Final patch the issue.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-50560?
The severity of CVE-2026-50560 is medium with a CVSS score of 6.9.
How do I fix CVE-2026-50560?
To fix CVE-2026-50560, upgrade to Netty versions 4.1.135.Final or 4.2.15.Final or later.
What kind of attack does CVE-2026-50560 expose my application to?
CVE-2026-50560 exposes applications to an HTTP/2 Reset Attack due to improper handling of max header sizes.
Which software is affected by CVE-2026-50560?
CVE-2026-50560 affects the Netty network application framework for developing protocol servers and clients.
When was CVE-2026-50560 published?
CVE-2026-50560 was published on June 12, 2026.