CVE-2021-212955.9MediumCWE-444

CVE-2021-21295: Possible request smuggling in HTTP/2 due missing validation

netty · io.netty:netty-codec-http2

Fixed in 4.1.60.Final · Affected: netty io.netty:netty-codec-http2 before 4.1.60.Final · Exploitation: likely to be exploited (10% or more)

Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.

18.9%probability of exploitation in the next 30 days

97th percentile

050100

Higher than 97% of scored CVEs

5.9MediumCVSS 3.1

LowMediumHighCrit.

DescriptionCVE.org

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`.

Affected products1

From the CVE record. A product or version that is not listed is unknown, not unaffected.

netty · io.netty:netty-codec-http2< 4.1.60.Final

On the Atlas

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Open the Atlas

Exploitation: Likely to be exploited (10% or more). EPSS gives it a 10% or higher chance of exploitation in the next 30 days.
CISA KEV: Not listed
Public check: No public nuclei template
Weakness: Inconsistent Interpretation of HTTP Requests · Injection and Smuggling
Vendor: netty
Published: March 2021
Band: Likely to be exploited (10% or more), March 2021

CoverageNo articles yet

No CyberSIXT article names CVE-2021-21295 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.

References

28 more references are in the CVE record.