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Vulnerability record · CVE-2021-21409 · published 30 March 2021

CVE-2021-21409: Netty http request smuggling vulnerability

Netty · Netty

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 4.1.61.Final there is a vulnerability that enables request smuggling. The content-length header is not correctly validated if the request only uses a single Http2HeaderFrame with the endStream set to to true. This could lead to request smuggling if the request is proxied to a remote peer and translated to HTTP/1.1. This is a followup of GHSA-wm47-8v5p-wjpj/CVE-2021-21295 which did miss to fix this one case. This was fixed as part of 4.1.61.Final.

5.9 CVSS 3.1 Medium EPSS 4.9% · top 8.2% CWE-444 · HTTP request smuggling
5.9CVSS 3.1 base score, v2 4.3
4.9%EPSS exploitation probability, 30 days
NoNot in CISA KEV
18Affected product versions listed by NVD
118References
17 Jun 2026Last modified by NVD

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 4.1.61.Final there is a vulnerability that enables request smuggling. The content-length header is not correctly validated if the request only uses a single Http2HeaderFrame with the endStream set to to true. This could lead to request smuggling if the request is proxied to a remote peer and translated to HTTP/1.1. This is a followup of GHSA-wm47-8v5p-wjpj/CVE-2021-21295 which did miss to fix this one case. This was fixed as part of 4.1.61.Final.

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected products

18 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-21295 Third Party Advisory
https://github.com/netty/netty/commit/b0fa4d5aab4215f3c22ce6123dd8dd5f38dc0432 PatchThird Party Advisory
https://github.com/netty/netty/security/advisories/GHSA-f256-j965-7f32 Third Party Advisory
https://github.com/netty/netty/security/advisories/GHSA-wm47-8v5p-wjpj Third Party Advisory
https://lists.apache.org/thread.html/r0b09f3e31e004fe583f677f7afa46bd30110904576c13c5ac818ac2c%40%3Cissues.flink.apache.
https://lists.apache.org/thread.html/r0ca82fec33334e571fe5b388272260778883e307e15415d7b1443de2%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/r101f82d8f3b5af0bf79aecbd5b2dd3b404f6bb51d1a54c2c3d29bed9%40%3Cnotifications.zookee
https://lists.apache.org/thread.html/r1b3cb056364794f919aaf26ceaf7423de64e7fdd05a914066e7d5219%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/r2732aa3884cacfecac4c54cfaa77c279ba815cad44b464a567216f83%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/r31044fb995e894749cb821c6fe56f487c16a97028e6e360e59f09d58%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/r4a98827bb4a7edbd69ef862f2351391845697c40711820d10df52ca5%40%3Ccommits.zookeeper.ap
https://lists.apache.org/thread.html/r4b8be87acf5b9c098a2ee350b5ca5716fe7afeaf0a21a4ee45a90687%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/r4ea2f1a9d79d4fc1896e085f31fb60a21b1770d0a26a5250f849372d%40%3Cissues.kudu.apache.o
https://lists.apache.org/thread.html/r584cf871f188c406d8bd447ff4e2fd9817fca862436c064d0951a071%40%3Ccommits.pulsar.apach
https://lists.apache.org/thread.html/r5baac01f9e06c40ff7aab209d5751b3b58802c63734e33324b70a06a%40%3Cissues.flink.apache.
https://lists.apache.org/thread.html/r5cbea8614812289a9b98d0cfc54b47f54cef424ac98d5e315b791795%40%3Cnotifications.zookee
https://lists.apache.org/thread.html/r5f2f120b2b8d099226473db1832ffb4d7c1d6dc2d228a164bf293a8e%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/r602e98daacc98934f097f07f2eed6eb07c18bfc1949c8489dc7bfcf5%40%3Cissues.flink.apache.
https://lists.apache.org/thread.html/r61564d86a75403b854cdafee67fc69c8b88c5f6802c2c838f4282cc8%40%3Ccommits.pulsar.apach
https://lists.apache.org/thread.html/r69efd8ef003f612c43e4154e788ca3b1f837feaacd16d97854402355%40%3Ccommits.zookeeper.ap
https://lists.apache.org/thread.html/r6dac9bd799ceac499c7a7e152a9b0dc7f2fe7f89ec5605d129bb047b%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/r70c3a7bfa904f06a1902f4df20ee26e4f09a46b8fd3eb304dc57a2de%40%3Cdev.zookeeper.apache
https://lists.apache.org/thread.html/r7879ddcb990c835c6b246654770d836f9d031dee982be836744e50ed%40%3Ccommits.pulsar.apach
https://lists.apache.org/thread.html/r7b54563abebe3dbbe421e1ba075c2030d8d460372f8c79b7789684b6%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/r823d4b27fcba8dad5fe945bdefce3ca5a0031187966eb6ef3cc22ba9%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/r855b4b6814ac829ce2d48dd9d8138d07f33387e710de798ee92c011e%40%3Cissues.flink.apache.
https://lists.apache.org/thread.html/r967002f0939e69bdec58f070735a19dd57c1f2b8f817949ca17cddae%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/r9ec78dc409f3f1edff88f21cab53737f36aad46f582a9825389092e0%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/r9fe840c36b74f92b8d4a089ada1f9fd1d6293742efa18b10e06b66d2%40%3Ccommits.zookeeper.ap
https://lists.apache.org/thread.html/ra64d56a8a331ffd7bdcd24a9aaaeeedeacd5d639f5a683389123f898%40%3Cdev.flink.apache.org
https://lists.apache.org/thread.html/ra655e5cec74d1ddf62adacb71d398abd96f3ea2c588f6bbf048348eb%40%3Cissues.kudu.apache.o
https://lists.apache.org/thread.html/ra66e93703e3f4bd31bdfd0b6fb0c32ae96b528259bb1aa2b6d38e401%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/raa413040db6d2197593cc03edecfd168732e697119e6447b0a25d525%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/rac8cf45a1bab9ead5c9a860cbadd6faaeb7792203617b6ec3874736d%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/rafc77f9f03031297394f3d372ccea751b23576f8a2ae9b6b053894c5%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/rba2a9ef1d0af882ab58fadb336a58818495245dda43d32a7d7837187%40%3Cissues.zookeeper.apa
https://lists.apache.org/thread.html/rbde2f13daf4911504f0eaea43eee4f42555241b5f6d9d71564b6c5fa%40%3Cjira.kafka.apache.or
https://lists.apache.org/thread.html/rca0978b634a0c3ebee4126ec29c7f570b165fae3f8f3658754c1cbd3%40%3Cissues.kudu.apache.o
https://lists.apache.org/thread.html/rcae42fba06979934208bbd515584b241d3ad01d1bb8b063512644362%40%3Cdev.zookeeper.apache
https://lists.apache.org/thread.html/rd4a6b7dec38ea6cd28b6f94bd4b312629a52b80be3786d5fb0e474bc%40%3Cissues.kudu.apache.o

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Source: NIST National Vulnerability Database (record CVE-2021-21409), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.