Medium 6.9Published Jul 29, 2026

CVE-2026-59900Netty codec-http2: Lack of Host Header Deduplication in HTTP/2→HTTP/1.x Translation Leads to Request Routing Bypass

Updated under an hour ago (Oct 27, 2026, 5:10 PM ET)

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Exploited in the last 30 days

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, Netty's HTTP/2-to-HTTP/1.x translation layer (`Http2StreamFrameToHttpObjectCodec` and `InboundHttp2ToHttpAdapter`) fails to deduplicate or validate `Host` headers when an HTTP/2 client supplies both the `:authority` pseudo-header and a literal `host` header in a single HEADERS frame. The translator maps `:authority` to `Host` and separately copies the literal `host` header, producing an `HttpRequest` object containing two `Host` headers with attacker-controlled differing values. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.

CVSS: 6.9 MEDIUM (v4.0, CNA)CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
Weakness (CWE): CWE-444
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Analyzed
Record last updated: Jul 29, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

netty netty netty:netty (from the name)	from 4.2.0.Final, < 4.2.16.Final; before 4.1.136.Final	CNA record
netty netty netty:netty	before 4.1.136; from 4.2.0 before 4.2.16	NVD

References

References

https://github.com/netty/netty/security/advisories/GHSA-c69g-56f8-xwqj	x-refsource-confirm, vendor-advisory
https://github.com/netty/netty/releases/tag/netty-4.1.136.Final	x-refsource-misc, release-notes
https://github.com/netty/netty/releases/tag/netty-4.2.16.Final	x-refsource-misc, release-notes

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.