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Vulnerability · Published Mar 9, 2021 · Assigned by GitHub_M

CVE-2021-21295Possible request smuggling in HTTP/2 due missing validation

Medium 5.9

In plain English

A medium-severity security flaw in io.netty:netty-codec-http2 from netty. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 18.9% (higher than 97% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.9Medium
Exploit odds (30 days)18.9%top 2.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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`.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12netty1:4.1.48-3DEBIAN-CVE-2021-21295
Debian:13netty1:4.1.48-3DEBIAN-CVE-2021-21295
Debian:14netty1:4.1.48-3DEBIAN-CVE-2021-21295
Mavenio.netty:nettyno fix listedGHSA-wm47-8v5p-wjpj
Mavenio.netty:netty-codec-http24.1.60.FinalGHSA-wm47-8v5p-wjpj
Mavenorg.jboss.netty:nettyno fix listedGHSA-wm47-8v5p-wjpj
Rocky Linux:8libdb0:5.3.28-42.el8_4RLSA-2022:5498
Ubuntu:22.04:LTSnetty1:4.1.48-4+deb11u1build0.22.04.1USN-6049-1
Ubuntu:22.04:LTSnetty1:4.1.48-4+deb11u1build0.22.04.1UBUNTU-CVE-2021-21295

Affected products (as reported)

VendorProductVersions
netty io.netty:netty-codec-http2 < 4.1.60.Final

Weakness: CWE-444 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

References