CVE Catalog

CVE-2026-18174

MediumCVSS 5.3
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.19%

9th percentile - higher than 9% of all known CVEs

Summary

@fastify/forwarded before version 3.0.2 incorrectly parses the X-Forwarded-For header when it 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, which can evade security decisions based on exact string matching, such as allowlists, blocklists, per-IP rate limit keys, or audit log correlation.

Risk Assessment

Applications relying on exact client IP matching (e.g., allowlists, blocklists, rate limiting) can be bypassed because the tab-corrupted IP does not match the expected value, potentially leading to unauthorized access or security bypass.

Recommendation

Update @fastify/forwarded to version 3.0.2 or later, which strips all whitespace as per RFC 7230.

Related vulnerabilities

Original NVD description (English source)

@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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS