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CVE-2026-33805

Fastify Fastify/http-proxy vulnerability

8.6 HIGHPublic exploitEPSS 0.56%
  1. Published15 Apr 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeChanged
ConfidentialityNone
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

Affected products

Fastify Fastify/http-proxy< 11.4.4
Fastify Reply-from< 12.6.2

Remediation

Fixed in
Fastify Fastify/http-proxy≥ 11.4.4
Fastify Reply-from≥ 12.6.2

References

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Frequently asked

Is CVE-2026-33805 being actively exploited?

CVE-2026-33805 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.56%.

How severe is CVE-2026-33805?

CVE-2026-33805 has a CVSS 3.1 base score of 8.6, rated high. EPSS estimates a 0.56% probability of exploitation.

Which products are affected by CVE-2026-33805?

Affected products include Fastify Fastify/http-proxy, Fastify Reply-from.

How do I fix CVE-2026-33805?

Upgrade affected software to a fixed version, for example Fastify Fastify/http-proxy 11.4.4, Fastify Reply-from 12.6.2 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-33805 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.