Medium severity · published Jul 29, 2026
CVE-2026-59900
Netty codec-http2: Lack of Host Header Deduplication in HTTP/2→HTTP/1.x Translation Leads to Request Routing Bypass
5.3
CVSS
0.4%
EPSS
No
On KEV
Description
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 vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 34% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
NE
netty · netty
>= 4.2.0.Final, < 4.2.16.Final; < 4.1.136.Final · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-59900
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-59900
Release Notes
https://github.com/netty/netty/releases/tag/netty-4.1.136.Final
Release Notes
https://github.com/netty/netty/releases/tag/netty-4.2.16.Final
Vendor Advisory
https://github.com/netty/netty/security/advisories/GHSA-c69g-56f8-xwqj
More from netty
7.5
CVE-2023-44487
HTTP/2 Rapid Reset Attack Vulnerability
10.0
CVE-2026-47691
Netty has Insufficient Bailiwick Validation for NS Records
10.0
CVE-2026-45674
Netty Vulnerable to DNS Cache Poisoning via Missing Bailiwick Checks in CNAME Records
9.8
CVE-2026-56817
Netty: XML External Entity (XXE) injection via unconfigured XML factory when DTD and entity processing are enabled
9.8
CVE-2026-42581
Netty: HTTP/1.0 TE+CL Coexistence Bypasses Smuggling Sanitization