CVE-2026-54340

HIGHPre-NVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.5%, top 59% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
7.5EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.5Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
7.5
EG Score
7.5(medium)
EG Risk
49(Track)
EG Risk 49/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity75% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
41%
KEV
Not listed

Published

July 16, 2026

Last Modified

August 5, 2026

Advisory Details (2)

Auto-updated Jul 17, 2026
Patch available. Sources: github_commit, github.
github Patch Available

HTTP/2 state amplification · Advisory · h2o/h2o · GitHub

https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9
github_commit

commit 9265bdd9a996 (h2o/h2o)

Fix landed in h2o/h2o commit 9265bdd9a996 — awaiting tagged release

https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063

Affected Packages

(2 across 2 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
h2o2.2.5+dfsg2-10 ... 2.2.5+dfsg2-9 (10 versions)——
Debian:12(1)
PackageVulnerable rangeFixed inDependents
h2o2.2.5+dfsg2-10 ... 2.2.5+dfsg2-9 (7 versions)——

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 7× in last 7d / 43× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-11 14:53 UTCEPSS rescore
  2. 2026-09-10 09:35 UTCEPSS rescore
  3. 2026-09-08 22:01 UTCEPSS rescore
  4. 2026-09-08 00:23 UTCEG score recompute
  5. 2026-09-07 16:01 UTCEPSS rescore
  6. 2026-09-06 13:47 UTCEPSS rescore
  7. 2026-09-05 20:32 UTCEG score recompute
  8. 2026-09-04 05:06 UTCEPSS rescore
  9. 2026-09-02 14:12 UTCEPSS rescore
  10. 2026-09-01 13:54 UTCEPSS rescore
  11. 2026-09-01 04:40 UTCEPSS rescore
  12. 2026-08-31 02:55 UTCEG score recompute
  13. 2026-08-30 19:17 UTCEPSS rescore
  14. 2026-08-30 03:27 UTCEG score recompute
  15. 2026-08-30 01:22 UTCEPSS rescore
  16. 2026-08-28 21:41 UTCEPSS rescore
  17. 2026-08-27 23:53 UTCEG score recompute
  18. 2026-08-27 14:25 UTCEPSS rescore
  19. 2026-08-26 23:00 UTCEG score recompute
  20. 2026-08-26 14:46 UTCEPSS rescore
  21. 2026-08-26 00:02 UTCEG score recompute
  22. 2026-08-25 13:49 UTCEPSS rescore
  23. 2026-08-24 14:47 UTCEG score recompute
  24. 2026-08-23 05:11 UTCEG score recompute
  25. 2026-08-23 00:19 UTCEPSS rescore
Show 66 more
  1. 2026-08-22 07:06 UTCEG score recompute
  2. 2026-08-21 23:49 UTCEPSS rescore
  3. 2026-08-21 09:00 UTCEG score recompute
  4. 2026-08-20 22:55 UTCEPSS rescore
  5. 2026-08-19 23:50 UTCEG score recompute
  6. 2026-08-19 17:04 UTCEPSS rescore
  7. 2026-08-18 20:37 UTCEG score recompute
  8. 2026-08-18 13:48 UTCEPSS rescore
  9. 2026-08-17 21:18 UTCEG score recompute
  10. 2026-08-17 13:47 UTCEPSS rescore
  11. 2026-08-16 20:33 UTCEG score recompute
  12. 2026-08-16 14:56 UTCEPSS rescore
  13. 2026-08-16 09:31 UTCEG score recompute
  14. 2026-08-16 02:14 UTCEPSS rescore
  15. 2026-08-15 11:27 UTCEG score recompute
  16. 2026-08-15 01:30 UTCEPSS rescore
  17. 2026-08-14 02:22 UTCEG score recompute
  18. 2026-08-13 22:00 UTCEPSS rescore
  19. 2026-08-12 17:15 UTCEG score recompute
  20. 2026-08-12 13:51 UTCEPSS rescore
  21. 2026-08-11 19:12 UTCEG score recompute
  22. 2026-08-11 08:11 UTCEG score recompute
  23. 2026-08-11 00:00 UTCEPSS rescore
  24. 2026-08-09 23:06 UTCEG score recompute
  25. 2026-08-09 13:46 UTCEPSS rescore
  26. 2026-08-09 01:03 UTCEG score recompute
  27. 2026-08-08 16:37 UTCEPSS rescore
  28. 2026-08-08 02:59 UTCEG score recompute
  29. 2026-08-06 17:55 UTCEG score recompute
  30. 2026-08-06 13:47 UTCEPSS rescore
  31. 2026-08-05 19:51 UTCEG score recompute
  32. 2026-08-05 19:17 UTCEPSS rescore
  33. 2026-08-04 18:59 UTCEG score recompute
  34. 2026-08-04 15:10 UTCEPSS rescore
  35. 2026-08-04 10:39 UTCEPSS rescore
  36. 2026-08-03 19:29 UTCEG score recompute
  37. 2026-08-03 10:36 UTCEPSS rescore
  38. 2026-08-02 10:15 UTCEG score recompute
  39. 2026-08-02 02:27 UTCEPSS rescore
  40. 2026-08-01 12:12 UTCEG score recompute
  41. 2026-08-01 04:16 UTCEPSS rescore
  42. 2026-07-31 03:03 UTCEG score recompute
  43. 2026-07-30 16:28 UTCEPSS rescore
  44. 2026-07-30 16:00 UTCEG score recompute
  45. 2026-07-30 04:14 UTCEG score recompute
  46. 2026-07-30 01:30 UTCEPSS rescore
  47. 2026-07-28 19:09 UTCEG score recompute
  48. 2026-07-28 15:37 UTCEPSS rescore
  49. 2026-07-27 20:51 UTCEG score recompute
  50. 2026-07-26 22:25 UTCEG score recompute
  51. 2026-07-26 14:54 UTCEPSS rescore
  52. 2026-07-26 11:23 UTCEG score recompute
  53. 2026-07-25 14:18 UTCEPSS rescore
  54. 2026-07-24 14:18 UTCEPSS rescore
  55. 2026-07-23 14:18 UTCEPSS rescore
  56. 2026-07-23 03:19 UTCEG score recompute
  57. 2026-07-22 14:08 UTCEPSS rescore
  58. 2026-07-21 15:25 UTCEPSS rescore
  59. 2026-07-20 17:08 UTCEPSS rescore
  60. 2026-07-19 14:31 UTCEPSS rescore
  61. 2026-07-19 14:31 UTCEPSS rescore
  62. 2026-07-19 02:32 UTCEG score recompute
  63. 2026-07-19 02:29 UTCEPSS rescore
  64. 2026-07-18 10:04 UTCEPSS rescore
  65. 2026-07-16 23:54 UTCEG score recompute
  66. 2026-07-16 23:54 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-54340?
CVE-2026-54340 is a high vulnerability published on July 16, 2026. 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,…
When was CVE-2026-54340 disclosed?
CVE-2026-54340 was first published in the National Vulnerability Database on July 16, 2026, with the most recent update on August 5, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-54340 actively exploited?
CVE-2026-54340 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 59.2% of all scored CVEs.
What is the CVSS score of CVE-2026-54340?
CVE-2026-54340 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-54340?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-54340, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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