CVE-2021-21295

    Dashboard / Vulnerabilities / CVE-2021-21295

    CVE-2021-21295

    Published: 9 Mar 2021Last Modified: 7 Aug 2026

    Summary:

    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`.

    References: 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, 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https://lists.apache.org/thread.html/r5baac01f9e06c40ff7aab209d5751b3b58802c63734e33324b70a06a%40%3Cissues.flink.apache.org%3E, https://lists.apache.org/thread.html/r5e66e286afb5506cdfe9bbf68a323e8d09614f6d1ddc806ed0224700%40%3Cjira.kafka.apache.org%3E, https://lists.apache.org/thread.html/r5fc5786cdd640b1b0a3c643237ce0011f0a08a296b11c0e2c669022c%40%3Cdev.kafka.apache.org%3E, https://lists.apache.org/thread.html/r602e98daacc98934f097f07f2eed6eb07c18bfc1949c8489dc7bfcf5%40%3Cissues.flink.apache.org%3E, https://lists.apache.org/thread.html/r67c4f90658fde875521c949448c54c98517beecdc7f618f902c620ec%40%3Cissues.zookeeper.apache.org%3E, https://lists.apache.org/thread.html/r67e6a636cbc1958383a1cd72b7fd0cd7493360b1dd0e6c12f5761798%40%3Cnotifications.zookeeper.apache.org%3E, https://lists.apache.org/thread.html/r6a122c25e352eb134d01e7f4fc4d345a491c5ee9453fef6fc754d15b%40%3Ccommits.zookeeper.apache.org%3E, 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https://lists.apache.org/thread.html/r855b4b6814ac829ce2d48dd9d8138d07f33387e710de798ee92c011e%40%3Cissues.flink.apache.org%3E, https://lists.apache.org/thread.html/r86cd38a825ab2344f3e6cad570528852f29a4ffdf56ab67d75c36edf%40%3Cissues.hbase.apache.org%3E, https://lists.apache.org/thread.html/r8bcaf7821247b1836b10f6a1a3a3212b06272fd4cde4a859de1b78cf%40%3Ccommits.servicecomb.apache.org%3E, https://lists.apache.org/thread.html/r8db1d7b3b9acc9e8d2776395e280eb9615dd7790e1da8c57039963de%40%3Cnotifications.zookeeper.apache.org%3E, https://lists.apache.org/thread.html/r9051e4f484a970b5566dc1870ecd9c1eb435214e2652cf3ea4d0c0cc%40%3Cjira.kafka.apache.org%3E, https://lists.apache.org/thread.html/r905b92099998291956eebf4f1c5d95f5a0cbcece2946cc46d32274fd%40%3Cdev.hbase.apache.org%3E, https://lists.apache.org/thread.html/r96ce18044880c33634c4b3fcecc57b8b90673c9364d63eba00385523%40%3Cjira.kafka.apache.org%3E, 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https://lists.apache.org/thread.html/rfff6ff8ffb31e8a32619c79774def44b6ffbb037c128c5ad3eab7171%40%3Cissues.zookeeper.apache.org%3E, https://github.com/netty/netty/security/advisories/GHSA-wm47-8v5p-wjpj, https://security.netapp.com/advisory/ntap-20210604-0003/, https://www.debian.org/security/2021/dsa-4885, https://github.com/Netflix/zuul/pull/980, https://github.com/netty/netty/commit/89c241e3b1795ff257af4ad6eadc616cb2fb3dc4, https://www.oracle.com/security-alerts/cpuapr2022.html

    Affected packages

    Package

    Name:

    Purl:

    Affected ranges

    Type: GIT

    Events:

    Affected versions

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High
    CVE-2021-21295 | CVE-DB