CVE-2026-33805

@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.

CVSS 4.0

9.0CVSS: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 3.1

8.6CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

EPSS

0.4% chance of exploitation in the next 30 days; higher than 38% of CVEs (scores of 2026-10-26)

CWEs

CWE-644, CWE-444

Published

2026-04-15

Modified

2026-10-26

Record from

the NVD, synced 2026-10-26

Affected

• fastify:fastify\/http-proxy
• fastify:reply-from

Packages (OSV)

References

• https://cna.openjsf.org/security-advisories.html
• https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37
• https://access.redhat.com/errata/RHSA-2026:10175
• https://access.redhat.com/security/cve/CVE-2026-33805
• https://bugzilla.redhat.com/show_bug.cgi?id=2458651

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