@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.

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Fixes

Solution

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Workaround

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History

Wed, 15 Apr 2026 15:15:00 +0000

Type Values Removed Values Added
First Time appeared Fastify
Fastify fastify-http-proxy
Fastify fastify-reply-from
Fastify-reply-from Project
Fastify-reply-from Project fastify-reply-from
Vendors & Products Fastify
Fastify fastify-http-proxy
Fastify fastify-reply-from
Fastify-reply-from Project
Fastify-reply-from Project fastify-reply-from

Wed, 15 Apr 2026 13:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Wed, 15 Apr 2026 10:45:00 +0000

Type Values Removed Values Added
Description @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.
Title @fastify/reply-from vulnerable to connection header abuse enabling stripping of proxy-added headers
Weaknesses CWE-644
References
Metrics cvssV4_0

{'score': 9, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-04-15T13:08:12.612Z

Reserved: 2026-03-23T19:48:48.714Z

Link: CVE-2026-33805

cve-icon Vulnrichment

Updated: 2026-04-15T13:07:59.414Z

cve-icon NVD

Status : Received

Published: 2026-04-15T11:16:34.990

Modified: 2026-04-15T14:16:15.507

Link: CVE-2026-33805

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-04-15T14:53:03Z

Weaknesses