CVE-2026-55213

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 60% 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 edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1, when h2o processes a QPACK instruction sent from the peer over HTTP/3, lib/http3/qpack.c might allocate an on-stack buffer as large as approximately 800 KB by calling alloca, which exceeds the default pthread stack size used by musl libc and causes the h2o server to crash with a segmentation fault while touching the guard page. This issue is fixed in commit edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1.

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
40%
KEV
Not listed

Published

July 10, 2026

Last Modified

July 13, 2026

Advisory Details (2)

Auto-updated Jul 10, 2026
Patch available. Sources: github_commit, github.
github Patch Available

musl libc stack overflow (QPACK) · Advisory · h2o/h2o · GitHub

https://github.com/h2o/h2o/security/advisories/GHSA-432c-8xmj-frmq
github_commit

commit edd7a120bfc4 (h2o/h2o)

Fix landed in h2o/h2o commit edd7a120bfc4 — awaiting tagged release

https://github.com/h2o/h2o/commit/edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1

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(1)

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

Data Freshness Timeline

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

Frequently asked(5)

What is CVE-2026-55213?
CVE-2026-55213 is a high vulnerability published on July 10, 2026. h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1, when h2o processes a QPACK instruction sent from the peer over HTTP/3, lib/http3/qpack.c might allocate an on-stack buffer as large as approximately 800 KB by calling…
When was CVE-2026-55213 disclosed?
CVE-2026-55213 was first published in the National Vulnerability Database on July 10, 2026, with the most recent update on July 13, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-55213 actively exploited?
CVE-2026-55213 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 60.2% of all scored CVEs.
What is the CVSS score of CVE-2026-55213?
CVE-2026-55213 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-55213?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-55213, 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.

Dependency Blast Radius

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