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Fencer Vulns
high 7.4

CVE-2026-33805 json

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

published 2026-04-15 6 mo ago modified 2026-10-26 13 d ago also GHSA-gwhp-pf74-vj37 , EUVD-2026-22877

cvss
7.4
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 38%
public exploits
0
none known

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.

Patch / fix

  • npm @fastify/reply-from 12.6.2
  • npm @fastify/http-proxy 11.4.4
  • @fastify/reply-from @fastify/reply-from 12.6.2
  • @fastify/reply-from @fastify/http-proxy 11.4.4
  • Red Hat Red Hat OpenShift Dev Spaces 3.27 1776795511

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-33805 updated cvss 7.4

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

  • Red Hat OpenShift AI 2.25 rhoai/odh-dashboard-rhel9 1791853525, rhoai/odh-mod-arch-model-registry-rhel9 1791853432
    fixed: vendor fix RHSA-2026:87410
  • Red Hat OpenShift Dev Spaces 3.27 devspaces 1776795511
    fixed: vendor fix RHSA-2026:10175
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-dashboard-rhel8, rhoai/odh-mod-arch-maas-rhel9, rhoai/odh-mod-arch-gen-ai-rhel9 Red Hat OpenShift AI 2.25 rhoai/odh-rhel9-operator 1792570619, rhoai/odh-vllm-cpu-rhel9 1792018436, rhoai/odh-modelmesh-rhel9 1790881700, rhoai/odh-operator-bundle 1792571069, rhoai/odh-vllm-cuda-rhel9 1791358976, rhoai/odh-vllm-rocm-rhel9 1791282503, +64 more Red Hat OpenShift Dev Spaces 3.27 devspaces 1776716842, devspaces 1776717247, devspaces 1776718438, devspaces 1776718450, devspaces 1776718480, devspaces 1776718585, +9 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
6 mo ago

Exploit prediction

0.44% chance of exploitation in the next 30 days, higher than 38% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 9.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N
CISA ADP 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
CNA 4.0 9.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 3.1 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N
CNA 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
GitHub 3.1 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

Affected packages

ecosystem package affected fixed in
npm @fastify/reply-from
<12.6.2
12.6.2
npm @fastify/http-proxy
<11.4.4
11.4.4

Affected products

  • @fastify/reply-from @fastify/reply-from
  • @fastify/reply-from @fastify/http-proxy
  • Red Hat Red Hat OpenShift Dev Spaces 3.27
  • Red Hat Red Hat OpenShift AI (RHOAI)

Classification

Weakness
  • CWE-644 Improper Neutralization of HTTP Headers for Scripting Syntax
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.