CVE-2021-21295 · AETERNAE Research

Disclosure summary

Netty is an open-source, asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients. In Netty (io.netty:netty-codec-http2) before version 4.1.60.Final there is a vulnerability that enables request smuggling. If a Content-Length header is present in the original HTTP/2 request, the field is not validated by `Http2MultiplexHandler` as it is propagated up. This is fine as long as the request is not proxied through as HTTP/1.1. If the request comes in as an HTTP/2 stream, gets converted into the HTTP/1.1 domain objects (`HttpRequest`, `HttpContent`, etc.) via `Http2StreamFrameToHttpObjectCodec `and then sent up to the child channel's pipeline and proxied through a remote peer as HTTP/1.1 this may result in request smuggling. In a proxy case, users may assume the content-length is validated somehow, which is not the case. If the request is forwarded to a backend channel that is a HTTP/1.1 connection, the Content-Length now has meaning and needs to be checked. An attacker can smuggle requests inside the body as it gets downgraded from HTTP/2 to HTTP/1.1. For an example attack refer to the linked GitHub Advisory. Users are only affected if all of this is true: `HTTP2MultiplexCodec` or `Http2FrameCodec` is used, `Http2StreamFrameToHttpObjectCodec` is used to convert to HTTP/1.1 objects, and these HTTP/1.1 objects are forwarded to another remote peer. This has been patched in 4.1.60.Final As a workaround, the user can do the validation by themselves by implementing a custom `ChannelInboundHandler` that is put in the `ChannelPipeline` behind `Http2StreamFrameToHttpObjectCodec`.

Source-reported weakness categories

CWE-444

Source-specific records & product guidance

Sources retain their own attribution and scoring. Follow the original record to confirm affected versions, fixed releases, and configuration conditions.

NIST National Vulnerability Database · NVD-CVE-2021-21295

Open original source · Updated Oct 08, 2026

Only CPE matches marked vulnerable=true are indexed. AND/OR platform conditions must be checked in the original NVD record.

Vendor	Product / association	Version / bounds
netty	netty	* {"versionEndExcluding":"4.1.60"}
netapp	oncommand_api_services	-
netapp	oncommand_workflow_automation	-
debian	debian_linux	10.0
quarkus	quarkus	* {"versionEndIncluding":"1.13.7"}
apache	kudu	* {"versionEndExcluding":"1.16.0"}
apache	zookeeper	3.5.9
oracle	communications_cloud_native_core_policy	1.14.0

Original records & references

PUBLISHED 2021-03-09T14:15:12-05:00
MODIFIED 2026-10-08T18:17:05-04:00
INGESTED 2026-10-10T20:50:20-04:00

CVE-2021-21295.

Disclosure summary

Source-reported weakness categories

Source-specific records & product guidance

Original records & references