CVE-2026-33805

Summary

@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.

Affected Software

Weaknesses

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

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: yes
  • Technical Impact: partial

Additional References

• https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37

@fastify/reply-from: @fastify/http-proxy: Fastify Reply From and HTTP Proxy: Security bypass via Connection header manipulation

Additional References

• https://access.redhat.com/security/cve/CVE-2026-33805
• https://bugzilla.redhat.com/show_bug.cgi?id=2458651
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33805.json
• https://access.redhat.com/errata/RHSA-2026:10175

References

• https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37
• https://cna.openjsf.org/security-advisories.html

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