PT-2026-33038 · @Fastify/Reply From · Fastify-Http-Proxy+1

Climba03003 + 3 · Published 2026-04-15 · Updated 2026-04-15 · CVE-2026-33805

Mitre

CVSS v4.0

9.0

Critical

AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N

@fastify/reply-from v12.6.1 and earlier and @fastify/http-proxy v11.4.3 and earlier process the client's Connection header after the proxy has added its own headers via rewriteRequestHeaders. This allows attackers to retroactively strip proxy-added headers from upstream requests by listing them in the Connection header value. Any header added by the proxy for routing, access control, or security purposes can be selectively removed by a client. @fastify/http-proxy is also affected as it delegates to @fastify/reply-from.

Upgrade to @fastify/reply-from v12.6.2 or @fastify/http-proxy v11.4.4 or later.

Exploit

Fix

Weakness Enumeration

CWE-644

Related Identifiers

CVE-2026-33805

Affected Products

Fastify-Http-Proxy

@Fastify/Reply-From

References · 5

• 🔥 https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37 · Exploit
• https://nvd.nist.gov/vuln/detail/CVE-2026-33805 · Security Note
• https://twitter.com/kom_256/status/2044361225279082497 · Twitter Post
• https://cna.openjsf.org/security-advisories.html · Note
• https://twitter.com/0dayPublishing/status/2044365047820849649 · Twitter Post