CVE-2026-33805 PUBLISHED

@fastify/reply-from vulnerable to connection header abuse enabling stripping of proxy-added headers

Assigner: openjs
Reserved: 23.03.2026 Published: 15.04.2026 Updated: 15.04.2026

@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.

Metrics

CVSS 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
CVSS Score: 9

Product Status

Vendor @fastify/reply-from
Product @fastify/reply-from
Versions Default: unaffected
  • affected from 0 to 12.6.2 (excl.)
  • Version 12.6.2 is unaffected
Vendor @fastify/reply-from
Product @fastify/http-proxy
Versions Default: unaffected
  • affected from 0 to 11.4.4 (excl.)
  • Version 11.4.4 is unaffected

Credits

  • FredKSchott reporter
  • mcollina remediation developer
  • UlisesGascon remediation reviewer
  • climba03003 remediation reviewer

References

Problem Types

  • CWE-644: Improper Neutralization of HTTP Headers for Scripting Syntax CWE