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CVE-2026-58055

5.4 · MEDIUM

nghttp2's nghttpx proxy through 1.69.0 forwards an HTTP/1.1 Upgrade request that also carries a Content-Length header and body onto reusable keep-alive backend connections, re-adding the Upgrade an…

Published Jun 28, 2026CWE-444EPSS 0.25%

Overview

CVE-2026-58055 is a medium-severity vulnerability. It was published on June 28, 2026 and has a CVSS 3.1 base score of 5.4 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 5.4, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

nghttp2's nghttpx proxy through 1.69.0 forwards an HTTP/1.1 Upgrade request that also carries a Content-Length header and body onto reusable keep-alive backend connections, re-adding the Upgrade and Connection headers while passing Content-Length verbatim. A backend that resolves the resulting ambiguous message in the attacker's favor enables HTTP request/response smuggling and cross-client response-queue poisoning.

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

GitHubgithub.com/bikini/exploitarium/tree/main/nghttp2-nghttpx-upgrade-queue-poison-pocGitHubgithub.com/nghttp2/nghttp2/commit/ab28105c4a0197da24f8bfc414bc116055249e1eRefwww.vulncheck.com/advisories/nghttp2-nghttpx-http-request-response-smuggling-via-upgrade-request-with-content-length

How CyberStrike helps

Frequently asked questions

What is CVE-2026-58055?

CVE-2026-58055 is a medium-severity vulnerability. It was published on June 28, 2026 and has a CVSS 3.1 base score of 5.4 (MEDIUM).

How severe is CVE-2026-58055?

This vulnerability has a CVSS 3.1 base score of 5.4, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-58055?

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-2026-58055?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-58055 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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