CVE-2026-100666
Description
A flaw was found in Netty's HttpServerCodec. A remote attacker can exploit this vulnerability to cause HTTP response desynchronization, leading to response splitting and potential information disclosure. By sending pipelined requests with informational headers followed by another request, the server misaligns outbound responses with queued inbound requests. Consequently, response data can be associated with the wrong request on reused connections, leading to the delivery of unintended content.
Statement
A flaw was found in Netty's HttpServerCodec where processing pipelined HTTP/1.1 requests with 1xx informational responses causes HTTP response desynchronization. When a client sends a GET request with an 'Expect: 100-continue' header followed by a HEAD request, the server misaligns outbound responses with inbound requests, resulting in response splitting and unsafe connection reuse. This can lead to unintended information disclosure on reused connections.
Mitigation
Update to io.netty:netty-codec-http version 4.2.17.Final or 4.1.137.Final or later, which fixes the response queue management in HttpServerCodec to properly pair responses with their originating requests.
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 | 7.3 | N/A | 7.3 |
| 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 | Low | N/A | Low |
| Integrity Impact | Low | N/A | Low |
| Availability Impact | Low | N/A | Low |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
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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