CVE-2026-18174

@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.

CVSS v3 5.3 MEDIUM

5.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 3.9 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact LOW

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://cna.openjsf.org/security-advisories.html
https://github.com/fastify/forwarded/security/advisories/GHSA-2849-m2w7-xm8f

Configurations

No configuration.

History

29 Jul 2026, 14:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-07-29 14:16

Updated : 2026-07-30 16:43

NVD link : CVE-2026-18174

Mitre link : CVE-2026-18174

CVE.ORG link : CVE-2026-18174

JSON object : View

Products Affected

No product.

CWE

CWE-20

Improper Input Validation

CWE-184

Incomplete List of Disallowed Inputs

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