What’s Vulnerable › Vulnerabilities

CVE-2026-33805: @fastify/reply-from vulnerable to connection header abuse enabling stripping of proxy-added headers

• Severity: high (CVSS 8.6 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-04-15 · updated 2026-10-26
• Weakness: CWE-644

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.

Affected products

• @fastify/http-proxy: before 11.4.4 — fixed in 11.4.4
• fastify-reply-from: before 12.6.2 — fixed in 12.6.2

How to fix

Upgrade to a fixed version: @fastify/http-proxy 11.4.4; fastify-reply-from 12.6.2. Check the vendor advisory for mitigations.

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
• https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33805.json

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