Summary
Netty susceptible to HTTP/2 Reset Attack with different on-the-wire signature
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 SETTINGS_MAX_HEADER_LIST_SIZE. 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.
Credit
Jonathan Looney (Engineering, Netflix)
Contact
Ashley Tolbert (Security, Netflix) - [email protected]
Impact
This is a DDoS attack similar to the HTTP/2 Rapid Reset Attack.
The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.
CVE-2026-50560 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.2.15.Final, 4.1.135.Final); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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When speaking with clients, Netty should potentially treat this as “advisory” and ignore it. It would be best to ignore the SETTINGS_MAX_HEADER_LIST_SIZE 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.
Frequently Asked Questions
- What is CVE-2026-50560? CVE-2026-50560 is a medium-severity allocation of resources without limits or throttling vulnerability in io.netty:netty-codec-http2 (maven), affecting versions >= 4.2.0.Final, <= 4.2.14.Final. It is fixed in 4.2.15.Final, 4.1.135.Final. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
- How severe is CVE-2026-50560? CVE-2026-50560 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of io.netty:netty-codec-http2 are affected by CVE-2026-50560? io.netty:netty-codec-http2 (maven) versions >= 4.2.0.Final, <= 4.2.14.Final is affected.
- Is there a fix for CVE-2026-50560? Yes. CVE-2026-50560 is fixed in 4.2.15.Final, 4.1.135.Final. Upgrade to this version or later.
- Is CVE-2026-50560 exploitable, and should I be worried? Whether CVE-2026-50560 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-50560 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-50560?
- Upgrade
io.netty:netty-codec-http2to 4.2.15.Final or later - Upgrade
io.netty:netty-codec-http2to 4.1.135.Final or later
- Upgrade