VulnerabilityPublished 26 Sep 2026Updated 17 Oct 2026

CVE-2026-100659: Netty's HTTP/3 codec

Affects nettySource GCVE Database

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Not known to be exploited · CVSS 6.5 Medium · fixed in 4.2.18 : update netty when convenient.

Data as of 11 Nov 2026, 23:24 UTC

CVSS 3.1 base score

6.5Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 14% 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:L/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation 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.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-7j27-hw46-m8m8

What to do

Affected software

Product	Affected	Fixed in
Mavenio.netty/netty-codec-http3`pkg:maven/io.netty/netty-codec-http3`Other threats	Affected >=4.2.0.Final <=4.2.17.Final	Fixed in–
Ubuntu Pro 14.04 LTSnetty`pkg:deb/ubuntu/netty?arch=source&distro=esm-infra-legacy/trusty`Other threats	Affected =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 LTSnetty`pkg:deb/ubuntu/netty?arch=source&distro=esm-apps-legacy/xenial`Other threats	Affected 1:3.2.6.Final-2 – 1:4.0.34-1ubuntu0.1~esm5 9 affected builds	Fixed in–
Ubuntu Pro 18.04 LTSnetty`pkg:deb/ubuntu/netty?arch=source&distro=esm-apps/bionic`Other threats	Affected 1:4.1.7-4 – 1:4.1.7-4ubuntu0.1~esm1 10 affected builds	Fixed in–
Ubuntu Pro 20.04 LTSnetty`pkg:deb/ubuntu/netty?arch=source&distro=esm-apps/focal`Other threats	Affected 1:4.1.33-1 – 1:4.1.45-1ubuntu0.1~esm7 10 affected builds	Fixed in–
Ubuntu Pro 22.04 LTSnetty`pkg:deb/ubuntu/netty?arch=source&distro=esm-apps/jammy`Other threats	Affected 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

A fix is available in Netty version 4.2.18.Final. Users should upgrade to this version or later to remediate the vulnerability. No other mitigation or temporary workaround is indicated by the vendor advisory.

Description

Netty's HTTP/3 codec versions 4.2.0.Final through 4.2.17.Final do not enforce the RFC 9114 requirement that the :authority pseudo-header and the literal host header, when both are present, must have the same value. This flaw allows a remote unauthenticated attacker to send a HEADERS frame with conflicting authority values, potentially bypassing routing, virtual-host, and access-control decisions. The issue is fixed in version 4.2.18.Final.

Impact

An attacker can send specially crafted HEADERS frames with conflicting :authority and host header values to bypass routing, virtual-host, and access-control decisions. This could lead to unauthorized access or misrouting of HTTP/3 traffic. The vulnerability does not require authentication and has a CVSS 3.1 score of 6.5 (medium severity), indicating a moderate impact on confidentiality and integrity but no impact on availability.

CWE-444Inconsistent Interpretation of HTTP Requests (HTTP Request Smuggling) (opens in a new tab)
Base weaknessOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.
Implementation
Use a web server that employs a strict HTTP parsing procedure, such as Apache.
Implementation
Use only SSL communication.
Implementation
Terminate the client session after each request.
OWASP Cheat Sheets
REST Assessment (opens in a new tab)
REST Security (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V13.2.5 (opens in a new tab)
Attack patterns
HTTP Response Smuggling (opens in a new tab)
HTTP Request Smuggling (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 18 Oct 2026, 01:58 UTC

WeaknessesCWE-444

Technical details

References

Community reviews

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