CVE-2026-47244: Netty HTTP/2: Advertised MAX_CONCURRENT_STREAMS are not enforced
Impact DefaultHttp2Connection.DefaultEndpoint initialises maxActiveStreams/maxStreams to Integer.MAXVALUE, and Http2Settings never inserts SETTINGSMAXCONCURRENTSTREAMS by default (Http2Settings.java:305-307 only clamps a user-supplied value). Unless the application explicitly calls initialSettings().maxConcurrentStreams(n), a Netty HTTP/2 server advertises no limit and enforces none locally. Each open stream allocates a DefaultStream object, PropertyMap slots, flow-controller state and IntObjectHashMap entry; with ~2^30 permissible odd stream IDs a single TCP connection can create hundreds of thousands of long-lived stream objects. This is also the precondition for CVE-2023-44487-style Rapid-Reset amplification, where the absence of a low concurrent cap multiplies backend work.
Resources https://www.rfc-editor.org/rfc/rfc7540.html#section-6.5.2
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, DefaultHttp2Connection.DefaultEndpoint initialises maxActiveStreams/maxStreams to Integer.MAXVALUE, and Http2Settings never inserts SETTINGSMAXCONCURRENTSTREAMS by default (Http2Settings.java:305-307 only clamps a user-supplied value). Unless the application explicitly calls initialSettings().maxConcurrentStreams(n), a Netty HTTP/2 server advertises no limit and enforces none locally. Each open stream allocates a DefaultStream object, PropertyMap slots, flow-controller state and IntObjectHashMap entry; with ~2^30 permissible odd stream IDs a single TCP connection can create hundreds of thousands of long-lived stream objects. This is also the precondition for CVE-2023-44487-style Rapid-Reset amplification, where the absence of a low concurrent cap multiplies backend work. Versions 4.1.135.Final and 4.2.15.Final patch the issue.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
maven/io.netty:netty-codec-http2to a version that resolves this vulnerability.Fixed in 4.1.135.Final - Upgrade
Upgrade
maven/io.netty:netty-codec-http2to a version that resolves this vulnerability.Fixed in 4.2.15.Final - Upgrade
Upgrade
Netty HTTP/2to a version that resolves this vulnerability.Fixed in 4.1.135.Final - Upgrade
Upgrade
Netty HTTP/2to a version that resolves this vulnerability.Fixed in 4.2.15.Final - Configuration
Ensure the application explicitly sets a cap by calling initialSettings().maxConcurrentStreams(n); otherwise DefaultHttp2Connection.DefaultEndpoint initializes maxActiveStreams/maxStreams to Integer.MAX_VALUE and Http2Settings does not insert SETTINGS_MAX_CONCURRENT_STREAMS by default, resulting in the server advertising no limit and enforcing none locally.
Netty HTTP/2 server initialSettings().maxConcurrentStreams(n) = n (set to a low, application-appropriate limit instead of leaving it unspecified)
Event History
Frequently Asked Questions
What is the severity of CVE-2026-47244?
CVE-2026-47244 has a medium severity score of 5.3.
What is the risk associated with CVE-2026-47244?
CVE-2026-47244 has a risk rating of 27.
How do I mitigate CVE-2026-47244?
To mitigate CVE-2026-47244, ensure your application explicitly sets the SETTINGS_MAX_CONCURRENT_STREAMS value in Http2Settings.
What component is affected by CVE-2026-47244?
CVE-2026-47244 affects the 'netty-codec-http2' component of the Maven repository.
When was CVE-2026-47244 published?
CVE-2026-47244 was published on June 8, 2026.