CVE-2021-21295
In Netty (io.netty:netty-codec-http2) before version 4.1.60.Final there is a vulnerability that enables request smuggling.
Does this matter?
EPSS puts the probability of exploitation in the next 30 days at 18.9%, higher than 97% of all known CVEs. Patch or mitigate before the next change window.
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 3.1
- 5.9 MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
- EPSS
- 18.89% probability · 97th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-444
- Affected
- netty/netty · netapp/oncommand api services · netapp/oncommand workflow automation · debian/debian linux · quarkus/quarkus · apache/kudu · apache/zookeeper · oracle/communications cloud native core policy
- Source
- security-advisories@github.com
EPSS 18.9% since 3 November 2026; no change recorded yet. The dashed line is the ten per cent mark our analysts treat as “patch before the next change window”. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://github.com/Netflix/zuul/pull/980Patch, Third Party Advisory
- https://github.com/netty/netty/commit/89c241e3b1795ff257af4ad6eadc616cb2fb3dc4Patch, Vendor Advisory
- https://github.com/netty/netty/security/advisories/GHSA-wm47-8v5p-wjpjThird Party Advisory
- 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
- https://lists.apache.org/thread.html/r04a3e0d9f53421fb946c60cc54762b7151dc692eb4e39970a7579052%40%3Ccommits.servicecomb.apache.org%3E
- https://lists.apache.org/thread.html/r0b09f3e31e004fe583f677f7afa46bd30110904576c13c5ac818ac2c%40%3Cissues.flink.apache.org%3E
- https://lists.apache.org/thread.html/r15f66ada9a5faf4bac69d9e7c4521cedfefa62df9509881603791969%40%3Cjira.kafka.apache.org%3E
- https://lists.apache.org/thread.html/r16c4b55ac82be72f28adad4f8061477e5f978199d5725691dcc82c24%40%3Ccommits.servicecomb.apache.org%3E
- https://lists.apache.org/thread.html/r1908a34b9cc7120e5c19968a116ddbcffea5e9deb76c2be4fa461904%40%3Cdev.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r1bca0b81193b74a451fc6d687ab58ef3a1f5ec40f6c61561d8dd9509%40%3Cissues.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r22adb45fe902aeafcd0a1c4db13984224a667676c323c66db3af38a1%40%3Ccommits.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r22b2f34447d71c9a0ad9079b7860323d5584fb9b40eb42668c21eaf1%40%3Cissues.hbase.apache.org%3E
- https://lists.apache.org/thread.html/r268850f26639ebe249356ed6d8edb54ee8943be6f200f770784fb190%40%3Cissues.hbase.apache.org%3E
- https://lists.apache.org/thread.html/r27b7e5a588ec826b15f38c40be500c50073400019ce7b8adfd07fece%40%3Cissues.hbase.apache.org%3E
- https://lists.apache.org/thread.html/r2936730ef0a06e724b96539bc7eacfcd3628987c16b1b99c790e7b87%40%3Cissues.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r2e93ce23e04c3f0a61e987d1111d0695cb668ac4ec4edbf237bd3e80%40%3Ccommits.servicecomb.apache.org%3E
- https://lists.apache.org/thread.html/r312ce5bd3c6bf08c138349b507b6f1c25fe9cf40b6f2b0014c9d12b1%40%3Cnotifications.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r32b0b640ad2be3b858f0af51c68a7d5c5a66a462c8bbb93699825cd3%40%3Cissues.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r33eb06b05afbc7df28d31055cae0cb3fd36cab808c884bf6d680bea5%40%3Cdev.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r393a339ab0b63ef9e6502253eeab26e7643b3e69738d5948b2b1d064%40%3Cissues.hbase.apache.org%3E
- https://lists.apache.org/thread.html/r3c293431c781696681abbfe1c573c2d9dcdae6fd3ff330ea22f0433f%40%3Cjira.kafka.apache.org%3E
- https://lists.apache.org/thread.html/r3c4596b9b37f5ae91628ccf169d33cd5a0da4b16b6c39d5bad8e03f3%40%3Cdev.jackrabbit.apache.org%3E
- https://lists.apache.org/thread.html/r3ff9e735ca33612d900607dc139ebd38a64cadc6bce292e53eb86d7f%40%3Cissues.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r490ca5611c150d193b320a2608209180713b7c68e501b67b0cffb925%40%3Ccommits.servicecomb.apache.org%3E
- https://lists.apache.org/thread.html/r4ea2f1a9d79d4fc1896e085f31fb60a21b1770d0a26a5250f849372d%40%3Cissues.kudu.apache.org%3E
- https://lists.apache.org/thread.html/r5232e33a1f3b310a3e083423f736f3925ebdb150844d60ac582809f8%40%3Cnotifications.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r5470456cf1409a99893ae9dd57439799f6dc1a60fda90e11570f66fe%40%3Cnotifications.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r57245853c7245baab09eae08728c52b58fd77666538092389cc3e882%40%3Ccommits.servicecomb.apache.org%3E
- https://lists.apache.org/thread.html/r584cf871f188c406d8bd447ff4e2fd9817fca862436c064d0951a071%40%3Ccommits.pulsar.apache.org%3E
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.