CVE-2026-54340h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3.
Updated under an hour ago ()
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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
- 7.5 HIGH (v3.1, NVD)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Weakness (CWE)
- CWE-400, CWE-770
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Not given
- NVD analysis
- Analyzed
- Record last updated
- Aug 5, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
h2o h2o h2o:h2o | from 2026-05-29 before 2026-06-04 | NVD |
References
- https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063patch
- https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9third-party-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.