CVE-2026-100663
Description
A flaw was found in Netty's HTTP/3 codec (netty-codec-http3). A remote attacker can bypass security policies and tunnel allowlists when Netty acts as an HTTP/1 to HTTP/3 proxy or gateway. Due to improper translation of HTTP/1 CONNECT requests, the component uses the attacker-controlled Host header to establish the HTTP/3 connection rather than the validated request target. By sending a request with conflicting destination headers, an attacker can route traffic to unauthorized backend services and circumvent egress filtering or audit controls.
Statement
This vulnerability is rated as having an Important severity because an unauthenticated remote attacker can circumvent egress policies and destination allow-lists if an application functions as an intermediary protocol proxy. Red Hat products incorporating the Netty HTTP/3 codec typically do not deploy services acting as HTTP/1 to HTTP/3 CONNECT gateways by default, which substantially limits practical exposure. However, custom deployments or services actively bridging these protocols may allow attackers to redirect tunneled traffic and evade backend routing restrictions.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | High | N/A | High |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Understanding the Weakness (CWE)
Integrity,Non-Repudiation,Access Control
Technical Impact: Unexpected State; Hide Activities; Bypass Protection Mechanism
An attacker could create HTTP messages to exploit a number of weaknesses including 1) the message can trick the web server to associate a URL with another URL's webpage and caching the contents of the webpage (web cache poisoning attack), 2) the message can be structured to bypass the firewall protection mechanisms and gain unauthorized access to a web application, and 3) the message can invoke a script or a page that returns client credentials (similar to a Cross Site Scripting attack).
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