Vulnerability in Fastify Fastify\/http-Proxy
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.6 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N.
EPSS exploit prediction
EPSS: 0.006 (45.5th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 45th percentile — 45.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.006 · change: +0.001
Affected products
- Fastify Fastify\/http-Proxy
- Fastify Reply-From
- @Fastify/reply-From @Fastify/http-Proxy — versions 0, 11.4.4
- @Fastify/reply-From — versions 0, 12.6.2
Weakness classification (CWE)
References
- ce714d77-add3-4f53-aff5-83d477b104bb (Exploit, Mitigation, Vendor Advisory)
- ce714d77-add3-4f53-aff5-83d477b104bb (Vendor Advisory)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Frequently asked questions
- What is CVE-2026-33805?
- CVE-2026-33805 is a high-severity vulnerability in Fastify Fastify\/http-Proxy, classified under Improper Neutralization of HTTP Headers for Scripting Syntax. CVSS score: 8.6/10. Published 2026-04-15.
- How severe is CVE-2026-33805?
- High severity. CVSS v3 base score is 8.6 out of 10.