CVE-2026-33805
Description
A flaw was found in @fastify/reply-from and @fastify/http-proxy. A remote attacker can exploit this vulnerability by manipulating the Connection header in client requests. This allows the attacker to remove specific headers that the proxy has added for security, routing, or access control purposes. Consequently, an attacker could bypass security mechanisms or gain unauthorized access to resources.
Statement
An Important flaw exists in @fastify/reply-from and @fastify/http-proxy, allowing a remote attacker to bypass security, routing, or access control mechanisms. This is achieved by manipulating the Connection header in client requests, which can remove critical proxy-added headers. If reply-from or http-proxy are being used to add security relevant headers the attacker may be able to remove such information resulting in authentication bypass, privilege escalations or the possibility of jeopardize any further security control which depends on the removed request headers. This vulnerability have a high attack complexity rate as the attacker needs to intercept the communication between the client and the server to be able to manipulate the headers.
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).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.4 | 8.6 | 7.4 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | High | Low | High |
| Privileges Required | None | None | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Changed | Unchanged |
| Confidentiality | High | None | High |
| Integrity Impact | High | High | High |
| Availability Impact | None | None | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/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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