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VulnerabilityPublished Updated

CVE-2026-100663: Netty's HTTP/3 codec (io.netty:netty-codec-http3) from 4.2.2.Final through 4.2.17.Final does not special-case HTTP/1 CONNECT authority-form

Affects nettySource GCVE Database

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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

CVSS 3.1 base score
7.5High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 23% 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:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 26 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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

ProductAffectedFixed in
Mavenio.netty/netty-codec-http3pkg:maven/io.netty/netty-codec-http3Other threatsAffected
  • >=4.2.2.Final <=4.2.17.Final
Fixed in–
Ubuntu Pro 14.04 LTSnettypkg:deb/ubuntu/netty?arch=source&distro=esm-infra-legacy/trustyOther threatsAffected
  • =1:3.2.6.Final-2
  • =1:3.2.6.Final-2+deb8u2build0.14.04.1~esm1
  • =1:3.2.6.Final-2+deb8u2ubuntu0.1~esm1
Fixed in–
Ubuntu Pro 16.04 LTSnettypkg:deb/ubuntu/netty?arch=source&distro=esm-apps-legacy/xenialOther threatsAffected
  • 1:3.2.6.Final-2 – 1:4.0.34-1ubuntu0.1~esm5
9 affected builds
Fixed in–
Ubuntu Pro 18.04 LTSnettypkg:deb/ubuntu/netty?arch=source&distro=esm-apps/bionicOther threatsAffected
  • 1:4.1.7-4 – 1:4.1.7-4ubuntu0.1~esm1
10 affected builds
Fixed in–
Ubuntu Pro 20.04 LTSnettypkg:deb/ubuntu/netty?arch=source&distro=esm-apps/focalOther threatsAffected
  • 1:4.1.33-1 – 1:4.1.45-1ubuntu0.1~esm7
10 affected builds
Fixed in–
Ubuntu Pro 22.04 LTSnettypkg:deb/ubuntu/netty?arch=source&distro=esm-apps/jammyOther threatsAffected
  • 1:4.1.48-4 – 1:4.1.48-4+deb11u2ubuntu0.2+esm1
10 affected builds
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 vulnerability is fixed. No other mitigation or temporary workaround is indicated in the available data.

Description

Netty's HTTP/3 codec versions 4.2.2.Final through 4.2.17.Final improperly handle HTTP/1 CONNECT authority-form request-targets during conversion to HTTP/3. This flaw allows an attacker to control the tunnel :authority in HTTP/3 CONNECT requests, potentially bypassing tunnel allow-lists, egress policies, backend selection, or audit controls. The issue is resolved in version 4.2.18.Final.

References

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