{"id":"UBUNTU-CVE-2021-21295","details":"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`.","modified":"2026-06-08T18:49:18.479790068Z","published":"2021-03-09T19:15:00Z","related":["USN-6049-1"],"upstream":["CVE-2021-21295"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2021-21295"},{"type":"REPORT","url":"https://github.com/netty/netty/security/advisories/GHSA-wm47-8v5p-wjpj"},{"type":"REPORT","url":"https://github.com/netty/netty/commit/89c241e3b1795ff257af4ad6eadc616cb2fb3dc4"},{"type":"REPORT","url":"https://github.com/Netflix/zuul/pull/980"},{"type":"ADVISORY","url":"https://ubuntu.com/security/notices/USN-6049-1"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2021-21295"}],"affected":[{"package":{"name":"netty","ecosystem":"Ubuntu:Pro:14.04:LTS","purl":"pkg:deb/ubuntu/netty?arch=source&distro=esm-infra-legacy%2Ftrusty"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1:3.2.6.Final-2","1:3.2.6.Final-2+deb8u2build0.14.04.1~esm1","1:3.2.6.Final-2+deb8u2ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"libnetty-java","binary_version":"1:3.2.6.Final-2+deb8u2ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-21295.json"}},{"package":{"name":"netty","ecosystem":"Ubuntu:Pro:16.04:LTS","purl":"pkg:deb/ubuntu/netty?arch=source&distro=esm-apps%2Fxenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:4.0.34-1ubuntu0.1~esm1"}]}],"versions":["1:3.2.6.Final-2","1:4.0.32-1","1:4.0.33-1","1:4.0.34-1"],"ecosystem_specific":{"binaries":[{"binary_name":"libnetty-java","binary_version":"1:4.0.34-1ubuntu0.1~esm1"}],"availability":"Available with Ubuntu Pro: https://ubuntu.com/pro"},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-21295.json"}},{"package":{"name":"netty","ecosystem":"Ubuntu:Pro:18.04:LTS","purl":"pkg:deb/ubuntu/netty?arch=source&distro=esm-apps%2Fbionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:4.1.7-4ubuntu0.1+esm2"}]}],"versions":["1:4.1.7-4","1:4.1.7-4ubuntu0.1~esm1","1:4.1.7-4ubuntu0.1","1:4.1.7-4ubuntu0.1+esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"libnetty-java","binary_version":"1:4.1.7-4ubuntu0.1+esm2"}],"availability":"Available with Ubuntu Pro: https://ubuntu.com/pro"},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-21295.json"}},{"package":{"name":"netty","ecosystem":"Ubuntu:Pro:20.04:LTS","purl":"pkg:deb/ubuntu/netty?arch=source&distro=esm-apps%2Ffocal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:4.1.45-1ubuntu0.1~esm1"}]}],"versions":["1:4.1.33-1","1:4.1.33-2","1:4.1.33-3","1:4.1.45-1"],"ecosystem_specific":{"availability":"Available with Ubuntu Pro: https://ubuntu.com/pro","binaries":[{"binary_version":"1:4.1.45-1ubuntu0.1~esm1","binary_name":"libnetty-java"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-21295.json"}},{"package":{"name":"netty","ecosystem":"Ubuntu:22.04:LTS","purl":"pkg:deb/ubuntu/netty?arch=source&distro=jammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:4.1.48-4+deb11u1build0.22.04.1"}]}],"versions":["1:4.1.48-4"],"ecosystem_specific":{"availability":"No subscription required","binaries":[{"binary_name":"libnetty-java","binary_version":"1:4.1.48-4+deb11u1build0.22.04.1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2021/UBUNTU-CVE-2021-21295.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N"},{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N"},{"type":"Ubuntu","score":"medium"}]}