CVE-2021-21295

Vulnerability 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`.

CVSS Score

Affected Products

Related Weaknesses (CWE)

References

• https://github.com/Netflix/zuul/pull/980PatchThird Party Advisory
• https://github.com/netty/netty/commit/89c241e3b1795ff257af4ad6eadc616cb2fb3dc4PatchVendor Advisory
• https://github.com/netty/netty/security/advisories/GHSA-wm47-8v5p-wjpjThird Party Advisory
• https://lists.apache.org/thread.html/r02e467123d45006a1dda20a38349e9c74c3a4b53e2
• https://lists.apache.org/thread.html/r040a5e4d9cca2f98354b58a70b27099672276f6699
• https://lists.apache.org/thread.html/r04a3e0d9f53421fb946c60cc54762b7151dc692eb4
• https://lists.apache.org/thread.html/r0b09f3e31e004fe583f677f7afa46bd30110904576
• https://lists.apache.org/thread.html/r15f66ada9a5faf4bac69d9e7c4521cedfefa62df95
• https://lists.apache.org/thread.html/r16c4b55ac82be72f28adad4f8061477e5f978199d5
• https://lists.apache.org/thread.html/r1908a34b9cc7120e5c19968a116ddbcffea5e9deb7
• https://lists.apache.org/thread.html/r1bca0b81193b74a451fc6d687ab58ef3a1f5ec40f6
• https://lists.apache.org/thread.html/r22adb45fe902aeafcd0a1c4db13984224a667676c3
• https://lists.apache.org/thread.html/r22b2f34447d71c9a0ad9079b7860323d5584fb9b40
• https://lists.apache.org/thread.html/r268850f26639ebe249356ed6d8edb54ee8943be6f2
• https://lists.apache.org/thread.html/r27b7e5a588ec826b15f38c40be500c50073400019c