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CVE-2026-33805

8.6 · HIGH

@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.

Published Apr 15, 2026CWE-644EPSS 0.56%

Overview

CVE-2026-33805 is a high-severity vulnerability. It was published on April 15, 2026 and has a CVSS 3.1 base score of 8.6 (HIGH).

This vulnerability has a CVSS 3.1 base score of 8.6, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refcna.openjsf.org/security-advisories.htmlGitHubgithub.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37Refaccess.redhat.com/errata/RHSA-2026:10175Refaccess.redhat.com/security/cve/CVE-2026-33805Refbugzilla.redhat.com/show_bug.cgi?id=2458651GitHubgithub.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37Refsecurity.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33805.json

How CyberStrike helps

Frequently asked questions

What is CVE-2026-33805?

CVE-2026-33805 is a high-severity vulnerability. It was published on April 15, 2026 and has a CVSS 3.1 base score of 8.6 (HIGH).

How severe is CVE-2026-33805?

This vulnerability has a CVSS 3.1 base score of 8.6, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-33805?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-33805?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-33805 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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