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CVE-2021-21409 Moderate

Possible request smuggling in HTTP/2 due missing validation of content-length

### Impact The content-length header is not correctly validated if the request only use 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 https://github.com/netty/netty/security/advisories/GHSA-wm47-8v5p-wjpj which did miss to fix this one case. ### Patches This was fixed as part of 4.1.61.Final ### Workarounds Validation can be done by the user before proxy the request by validating the header.

Exploit probability 4.9%
Published March 30, 2021
Required by Not available
Last source change February 4, 2026

02 / AFFECTED SOFTWARE

Affected packages

Unknown Unknown

112 explicit affected versions

Maven io.netty:netty

71 explicit affected versions

Maven io.netty:netty-codec-http2

73 explicit affected versions

Maven org.jboss.netty:netty

39 explicit affected versions

03 / CONNECTIONS

Connected vulnerabilities

04 / EVIDENCE

Source records

Open Source Vulnerabilities GHSA-f256-j965-7f32

### Impact The content-length header is not correctly validated if the request only use 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 https://github.com/netty/netty/security/advisories/GHSA-wm47-8v5p-wjpj which did miss to fix this one case. ### Patches This was fixed as part of 4.1.61.Final ### Workarounds Validation can be done by the user before proxy the request by validating the header.

View original source
Open Source Vulnerabilities CVE-2021-21409

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.

View original source

05 / REFERENCES

Further evidence