fastify fastify-forwarded up to 3.0.1 input validation

Summaryinfo

A vulnerability has been found in fastify fastify-forwarded up to 3.0.1 and classified as critical. Affected is an unknown function. This manipulation causes input validation. This vulnerability appears as CVE-2026-18174. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability was found in fastify fastify-forwarded up to 3.0.1. It has been declared as critical. Affected by this vulnerability is an unknown part. The manipulation with an unknown input leads to a input validation vulnerability. The CWE definition for the vulnerability is CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. As an impact it is known to affect integrity, and availability. The summary by CVE is:

@fastify/forwarded resolves client addresses from the X-Forwarded-For header. In versions before 3.0.2, when the header contains two or more comma separated entries, the parser trims only space characters and does not strip horizontal tabs, even though RFC 7230 defines optional whitespace as both space and tab. As a result, an entry padded with a tab keeps the literal tab in the resolved address string. Applications that make exact string match security decisions on the resolved client IP, such as an allowlist, a blocklist, a per IP rate limit key, or audit log correlation, can be evaded because the tab corrupted string no longer matches the expected value. This does not cross the trust boundary, since a tab corrupted string is not a valid IP and cannot be mistaken for a trusted proxy. The issue is fixed in @fastify/forwarded 3.0.2.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-18174 since 07/28/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available.

Upgrading to version 3.0.2 eliminates this vulnerability.

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Productinfo

Vendor

• fastify

Name

• fastify-forwarded

Version

• 3.0.0
• 3.0.1

CPE 2.3info

• 🔒
• 🔒

CPE 2.2info

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• 🔒

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