CVE-2026-54340
7.5 · HIGHOverview
CVE-2026-54340 is a high-severity vulnerability affecting h2o h2o. It was published on July 17, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).
This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
Technical Description
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 9265bdd, there is an HTTP/2 state amplification issue that combines HPACK decompression amplification with Slowloris-style stream stalling. Amplified decoded header state can be retained by stalled HTTP/2 streams, and depending on the configuration, additional limits are needed to bound decoded header state and prevent attack. This issue has been fixed by commit 9265bdd.
Remediation
Check the references section for vendor advisories and patches from h2o. Update h2o to the latest patched version. 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.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| h2o | h2o | >= 2026-05-29, < 2026-06-04 | Affected |
Frequently Asked Questions
What is CVE-2026-54340?
CVE-2026-54340 is a high-severity vulnerability affecting h2o h2o. It was published on July 17, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).
How severe is CVE-2026-54340?
This vulnerability has a CVSS 3.1 base score of 7.5, 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-2026-54340?
Check the references section for vendor advisories and patches from h2o. Update h2o to the latest patched version. 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-2026-54340?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-54340 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
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