{"cve":"CVE-2021-21295","nvd":{"published":"2021-03-09T19:15:12.657","modified":"2026-10-08T22:17:05.327","status":"Modified","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_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N","score":5.9},"cwes":["CWE-444"],"references":["https://github.com/Netflix/zuul/pull/980","https://github.com/netty/netty/commit/89c241e3b1795ff257af4ad6eadc616cb2fb3dc4","https://github.com/netty/netty/security/advisories/GHSA-wm47-8v5p-wjpj","https://lists.apache.org/thread.html/r02e467123d45006a1dda20a38349e9c74c3a4b53e2e07be0939ecb3f%40%3Cdev.ranger.apache.org%3E","https://lists.apache.org/thread.html/r040a5e4d9cca2f98354b58a70b27099672276f66995c4e2e39545d0b%40%3Cissues.hbase.apache.org%3E"],"products":["apache:kudu","apache:zookeeper","debian:debian_linux","netapp:oncommand_api_services","netapp:oncommand_workflow_automation","netty:netty","oracle:communications_cloud_native_core_policy","quarkus:quarkus"],"source":"nvd","synced_at":"2026-10-19T21:15:50.279857260+00:00"},"epss":{"cve":"CVE-2021-21295","score":0.18891,"percentile":0.97272,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-wm47-8v5p-wjpj","url":"https://osv.dev/vulnerability/GHSA-wm47-8v5p-wjpj","summary":"Possible request smuggling in HTTP/2 due missing validation","modified":"2026-09-10T03:48:43.368978975Z","packages":[{"ecosystem":"Maven","name":"io.netty:netty-codec-http2","purl":"pkg:maven/io.netty/netty-codec-http2","ranges":[">=4.0.0 <4.1.60.Final"],"fixed":["4.1.60.Final"]},{"ecosystem":"Maven","name":"org.jboss.netty:netty","purl":"pkg:maven/org.jboss.netty/netty","ranges":["all versions"],"fixed":[]},{"ecosystem":"Maven","name":"io.netty:netty","purl":"pkg:maven/io.netty/netty","ranges":["all versions"],"fixed":[]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}