CVE-2021-21295

Published: 9 March 2021

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`.

Priority

Cvss 3 Severity Score

5.9

Score breakdown

Status

Package	Release	Status
netty Launchpad, Ubuntu, Debian	hirsute	Ignored (end of life)
	trusty	Needs triage
	upstream	Needs triage
	bionic	Released (1:4.1.7-4ubuntu0.1+esm2) Available with Ubuntu Pro
	focal	Released (1:4.1.45-1ubuntu0.1~esm1) Available with Ubuntu Pro
	groovy	Ignored (end of life)
	impish	Ignored (end of life)
	lunar	Needs triage
	jammy	Released (1:4.1.48-4+deb11u1build0.22.04.1)
	kinetic	Released (1:4.1.48-5ubuntu0.1)
	xenial	Released (1:4.0.34-1ubuntu0.1~esm1) Available with Ubuntu Pro

Severity score breakdown

Parameter	Value
Base score	5.9
Attack vector	Network
Attack complexity	High
Privileges required	None
User interaction	None
Scope	Unchanged
Confidentiality	None
Integrity impact	High
Availability impact	None
Vector	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

References

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