CVE•Published 2026-04-15•Modified 2026-07-15•1 article on news•6 live references•NVD data

CVE-2026-33805Fastify · Fastify\/http-proxy

Vulnerability data via NVD (ingested)

CVSS v3.1

8.6

HIGH

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

EPSS percentile

Exploit Prediction Scoring System · top 64% of all CVEs

Weaknesses (CWE)

CWE-644Improper Neutralization of HTTP Headers for Scripting Syntax CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

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.

Timeline

Published 2026-04-15

Modified 2026-07-15

External references

NVD MITRE Exploit-DB GitHub PoC trickest/cve VulnCheck

Search for exposed instances

Shodan + Censys queries derived from NVD's CPE data. The vuln tag catches assets Shodan has explicitly linked to this CVE; the product / banner fingerprints find exposed instances even when the vuln tag was never applied (which is common).

Shodan · vuln tag0 hosts

vuln:CVE-2026-33805

Hosts Shodan has explicitly fingerprinted as vulnerable.

Shodan · product

product:"Fastify Fastify\/http-proxy"

All exposed Fastify Fastify\/http-proxy instances — cross-reference with the CVE's affected-version range.

Shodan · banner/body mention

http.html:"Fastify\/http-proxy"

HTTP body or banner mentions "Fastify\/http-proxy" — catches deploys Shodan didn't identify as a product.

More intel sources (5)

Shodan report

vuln:CVE-2026-33805