CVE-2026-33805: @fastify/reply-from v12.6.1 and earlier and @fastify/http-proxy v11.4.3 and earlier process the client's Conne

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HIGH 8.6REMOTEUPGRADEUPGRADE

CVE-2026-33805 is a high-severity flaw (CVSS 8.6) affecting fastify\/http-proxy, reply-from. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

@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. @f

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	8.6 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 62%)
CISA exploited list	No
Weakness	CWE-644, CWE-444
Published	2026-04-15
Last modified	2026-10-26

Publisher (CNA): openjs · Vendor: fastify

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-15 11:16 UTCPublished CVE record published
2026-10-26 22:10 UTCUpdated Record last modified

fastify fastify\/http-proxy UPGRADE

Affected: < 11.4.4

Fixed in: 11.4.4

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls fastifyhttp-proxy

2. UPGRADE to 11.4.4

npm install fastifyhttp-proxy@">=11.4.4"

fastify reply-from UPGRADE

Affected: < 12.6.2

Fixed in: 12.6.2

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls reply-from

2. UPGRADE to 12.6.2

npm install reply-from@">=12.6.2"

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-33805?

fastify\/http-proxy: upgrade to 11.4.4; reply-from: upgrade to 12.6.2. Exact commands for each OS are on this page.

Is CVE-2026-33805 being exploited?

CVE-2026-33805 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-33805 affect?

CVE-2026-33805 affects fastify\/http-proxy, reply-from. Severity is high (CVSS 8.6). @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 pro

How urgent is CVE-2026-33805?

Priority 50/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-85124 HIGH 7.5 UPGRADE @fastify/http-proxy versions before 11.6.2 do not validate proxied HTTP request paths for backslash based dot-
CVE-2026-15631 HIGH 8.7 UPGRADE Impact: @fastify/http-proxy versions from 9.4.0 up to and including 11.5.0 fail to validate the resolved WebSo
CVE-2026-16117 CRITICAL 10.0 UPGRADE Impact: @fastify/http-proxy versions up to and including 11.5.0 fail to rewrite the request prefix when the pr

References

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