CVE-2026-100664: Netty's HTTP/3 codec (io.netty:netty-codec-http3) versions 4.2.2.Final through 4.2.17.Final builds the HTTP/3 :authority pseudo-header from the
Affects nettySource GCVE Database
Not known to be exploited · CVSS 7.5 High · fixed in 4.2.18 : patch netty soon.
Data as of 10 Nov 2026, 23:24 UTC
- EPSS
- 0.3% chance of exploitation in 30 days – higher than 26% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 4.2.18
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:NExploitation evidence
Disclosed: evidence found.
CVE published 26 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 11 Nov 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Mavenio.netty/netty-codec-http3pkg:maven/io.netty/netty-codec-http3Other threats | Affected
| Fixed in– |
Ubuntu Pro 14.04 LTSnettypkg:deb/ubuntu/netty?arch=source&distro=esm-infra-legacy/trustyOther threats | Affected
| Fixed in– |
Ubuntu Pro 16.04 LTSnettypkg:deb/ubuntu/netty?arch=source&distro=esm-apps-legacy/xenialOther threats | Affected
| Fixed in– |
Ubuntu Pro 18.04 LTSnettypkg:deb/ubuntu/netty?arch=source&distro=esm-apps/bionicOther threats | Affected
| Fixed in– |
Ubuntu Pro 20.04 LTSnettypkg:deb/ubuntu/netty?arch=source&distro=esm-apps/focalOther threats | Affected
| Fixed in– |
Ubuntu Pro 22.04 LTSnettypkg:deb/ubuntu/netty?arch=source&distro=esm-apps/jammyOther threats | Affected
| Fixed in– |
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
Upgrade to Netty version 4.2.18.Final or later, where this issue is fixed. No other mitigation is indicated by the vendor advisory.
Description
Netty's HTTP/3 codec versions 4.2.2.Final through 4.2.17.Final improperly prioritize the HTTP/1 Host header over the authority in an absolute-form HTTP/1 request-target when building the HTTP/3 :authority pseudo-header. This violates HTTP/1.1 rules and can cause authority confusion in HTTP/1-to-HTTP/3 gateways or proxies, potentially leading to incorrect virtual-host routing, allow-list checks, backend selection, cache key usage, and URL generation. The vulnerability impacts data integrity but does not affect code execution or availability. The issue is fixed in version 4.2.18.Final.
References
- github.com/netty/netty/security/advisories/GHSA-hfr2-x62w-v49h (opens in a new tab)
- nvd.nist.gov/vuln/detail/CVE-2026-100664 (opens in a new tab)
- vulncheck.com/advisories/netty-4.2.2-through-4.2.15-http-1-host-header-authority-confusion (opens in a new tab)
- ubuntu.com/security/CVE-2026-100664 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-100664 (opens in a new tab)