---
cve: "CVE-2026-54340"
severity: "HIGH"
cvss: 7.5
epss: "28%"
vendor: "h2o"
kev: false
exploited: false
published: "2026-07-17 00:16:25"
tags: [cve, security, high]
source: tsecurity.de CVE-Dossier
exported: "2026-09-02T12:46:17+02:00"
---

# CVE-2026-54340

> 7.5 HIGH · 🧪 PoC

## Beschreibung

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.

## CVSS-Vektor

```
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |
| S Scope | Unverändert | good |
| C Vertraulichkeit | Keine | good |
| I Integrität | Keine | good |
| A Verfügbarkeit | Hoch | bad |

## Patch verfügbar (OSV)

- 9265bdd9a996ed992681055e3996baf3e09d2063 (Commit)

## Referenzen

- <https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9>
- <https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-54340) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_