GHSA-wm47-8v5p-wjpj: io.netty:netty-codec-http2 (CVE-2021-21295)

Package	Ecosystem	Affected	Fixed in
io.netty:netty-codec-http2	Maven	>=4.0.0, <4.1.60.Final	4.1.60.Final
org.jboss.netty:netty	Maven	all versions	No fixed version yet
io.netty:netty	Maven	all versions	No fixed version yet

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Netty's io.netty:netty-codec-http2 versions from 4.0.0 before 4.1.60.Final do not validate the Content-Length header on HTTP/2 requests. An attacker who can send HTTP/2 requests to a proxy that converts them to HTTP/1.1 and forwards them to a remote peer can smuggle requests inside the body. Upgrade to io.netty:netty-codec-http2 4.1.60.Final or later. Users can instead add a custom ChannelInboundHandler behind Http2StreamFrameToHttpObjectCodec that performs the Content-Length validation. No fixed version is listed for org.jboss.netty:netty or io.netty:netty.

Written 2 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
5.9	Medium	3.1	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N	CNA (GitHub_M)

CISA KEV Not listed.
EPSS 0.19, the 97th percentile, on 8 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:18 UTC First seen by agentprime
31 Oct 2026, 14:18 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.