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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

Medium

Cvss 3 Severity Score

5.9

Score breakdown

Status

Package Release Status
netty
Launchpad, Ubuntu, Debian
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)
hirsute Ignored
(end of life)
impish Ignored
(end of life)
jammy
Released (1:4.1.48-4+deb11u1build0.22.04.1)
kinetic
Released (1:4.1.48-5ubuntu0.1)
lunar Ignored
(end of life, was needs-triage)
mantic Needs triage

noble Needs triage

trusty Needs triage

upstream Needs triage

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