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Vulnerability record · CVE-2026-54340 · published 17 July 2026

CVE-2026-54340: H2o uncontrolled resource consumption vulnerability

H2o · H2o

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.

7.5 CVSS 3.1 High EPSS 0.49% · top 60.1% CWE-400 · Uncontrolled resource consumptionCWE-770 · Allocation without limits
7.5CVSS 3.1 base score
0.49%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
5 Aug 2026Last modified by NVD

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.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063 Patch
https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9 Third Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2026-3960H2o code injection vulnerabilityA critical remote code execution vulnerability exists in the unauthenticated REST API endpoint /99/ImportSQLTable in H2O-3 version 3.46.0.9 and prior…EPSS 1.0%9.8CVE-2025-6544H2o deserialization of untrusted data vulnerabilityA deserialization vulnerability exists in h2oai/h2o-3 versions <= 3.46.0.8, allowing attackers to read arbitrary system files and execute arbitrary c…EPSS 0.92%9.8CVE-2024-10553H2o deserialization of untrusted data vulnerabilityA vulnerability in the h2oai/h2o-3 REST API versions 3.46.0.4 allows unauthenticated remote attackers to execute arbitrary code via deserialization o…EPSS 1.6%9.8CVE-2023-6016H2o code injection vulnerabilityAn attacker is able to gain remote code execution on a server hosting the H2O dashboard through it's POJO model import feature.EPSS 31%9.1CVE-2024-45758H2o deserialization of untrusted data vulnerabilityH2O.ai H2O through 3.46.0.4 allows attackers to arbitrarily set the JDBC URL, leading to deserialization attacks, file reads, and command execution. …EPSS 0.91%8.2CVE-2024-8616H2o vulnerabilityIn h2oai/h2o-3 version 3.46.0, the `/99/Models/{name}/json` endpoint allows for arbitrary file overwrite on the target server. The vulnerability aris…EPSS 0.55%8.2CVE-2023-6569H2o vulnerabilityExternal Control of File Name or Path in h2oai/h2o-3EPSS 0.72%7.5CVE-2026-44453H2o allocation without limits vulnerabilityh2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 6b5370d, h2o is vulnerable to a Denial of Service attack when cal…EPSS 0.49%

Source: NIST National Vulnerability Database (record CVE-2026-54340), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.