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% (39th percentile of EPSS-scored CVEs). 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 mitigationSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.5%CVSS: 7.5Exploit: None knownExposed services: Not assessed

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

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
7.5HIGHmedium confidence
EG Risk
49
EG Risk 49/100CISA SSVC

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%
CISA SSVC: Track at low or medium mission impact; Attend at high (mission-essential systems).
Action: No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix.
EPSS PROB
0.5%
EPSS %ILE
40th
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Attend at high (mission-essential systems).

No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix.

Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

July 10, 2026

Last Modified

July 13, 2026

Advisory Details (2)

Auto-updated Jul 10, 2026
No fix on record yet. Sources: github_commit, github.
githubMentions a patch (unverified)

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 rangeFix by version rangeDependents
h2o2.2.5+dfsg2-10 ... 2.2.5+dfsg2-9 (10 versions)
  • every version on: no fix on record
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
h2o2.2.5+dfsg2-10 ... 2.2.5+dfsg2-9 (7 versions)
  • every version on: no fix on record
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 7× in last 7d / 33× 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.

Showing the most recent 100 of 129 total refreshes for this CVE.

  1. 2026-10-09 20:07 UTCEPSS rescore
  2. 2026-10-08 17:12 UTCEPSS rescore
  3. 2026-10-07 23:48 UTCEPSS rescore
  4. 2026-10-06 15:18 UTCEPSS rescore
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  6. 2026-10-04 23:22 UTCEPSS rescore
  7. 2026-10-03 14:26 UTCEPSS rescore
  8. 2026-10-02 17:56 UTCEPSS rescore
  9. 2026-10-01 19:50 UTCEPSS rescore
  10. 2026-10-01 14:57 UTCEG score recompute
  11. 2026-09-30 15:03 UTCEPSS rescore
  12. 2026-09-29 15:22 UTCEPSS rescore
  13. 2026-09-28 13:51 UTCEPSS rescore
  14. 2026-09-28 09:45 UTCEG score recompute
  15. 2026-09-27 13:48 UTCEPSS rescore
  16. 2026-09-26 15:59 UTCEPSS rescore
  17. 2026-09-24 14:04 UTCEPSS rescore
  18. 2026-09-24 11:09 UTCEG score recompute
  19. 2026-09-23 17:54 UTCEPSS rescore
  20. 2026-09-23 05:44 UTCEG score recompute
  21. 2026-09-20 20:16 UTCEPSS rescore
  22. 2026-09-18 19:28 UTCEPSS rescore
  23. 2026-09-18 05:17 UTCEG score recompute
  24. 2026-09-17 19:31 UTCEPSS rescore
  25. 2026-09-16 14:08 UTCEPSS rescore
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  1. 2026-09-16 05:15 UTCEPSS rescore
  2. 2026-09-15 03:11 UTCEPSS rescore
  3. 2026-09-13 23:38 UTCEG score recompute
  4. 2026-09-13 16:47 UTCEPSS rescore
  5. 2026-09-12 15:40 UTCEG score recompute
  6. 2026-09-12 02:43 UTCEG score recompute
  7. 2026-09-11 14:53 UTCEPSS rescore
  8. 2026-09-10 09:35 UTCEPSS rescore
  9. 2026-09-08 22:01 UTCEPSS rescore
  10. 2026-09-08 02:44 UTCEG score recompute
  11. 2026-09-07 16:01 UTCEPSS rescore
  12. 2026-09-06 13:56 UTCEG score recompute
  13. 2026-09-06 13:47 UTCEPSS rescore
  14. 2026-09-05 21:40 UTCEG score recompute
  15. 2026-09-04 05:06 UTCEPSS rescore
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  17. 2026-09-01 13:54 UTCEPSS rescore
  18. 2026-09-01 04:40 UTCEPSS rescore
  19. 2026-08-30 19:17 UTCEPSS rescore
  20. 2026-08-30 06:11 UTCEG score recompute
  21. 2026-08-30 01:22 UTCEPSS rescore
  22. 2026-08-28 21:41 UTCEPSS rescore
  23. 2026-08-27 21:39 UTCEG score recompute
  24. 2026-08-27 14:25 UTCEPSS rescore
  25. 2026-08-27 00:44 UTCEG score recompute
  26. 2026-08-26 14:46 UTCEPSS rescore
  27. 2026-08-26 03:31 UTCEG score recompute
  28. 2026-08-25 13:49 UTCEPSS rescore
  29. 2026-08-24 23:38 UTCEG score recompute
  30. 2026-08-24 10:40 UTCEG score recompute
  31. 2026-08-23 08:35 UTCEG score recompute
  32. 2026-08-23 00:19 UTCEPSS rescore
  33. 2026-08-22 06:40 UTCEG score recompute
  34. 2026-08-21 23:49 UTCEPSS rescore
  35. 2026-08-21 04:46 UTCEG score recompute
  36. 2026-08-20 22:55 UTCEPSS rescore
  37. 2026-08-20 02:52 UTCEG score recompute
  38. 2026-08-19 17:04 UTCEPSS rescore
  39. 2026-08-19 00:43 UTCEG score recompute
  40. 2026-08-18 13:48 UTCEPSS rescore
  41. 2026-08-17 22:11 UTCEG score recompute
  42. 2026-08-17 13:47 UTCEPSS rescore
  43. 2026-08-16 19:34 UTCEG score recompute
  44. 2026-08-16 14:56 UTCEPSS rescore
  45. 2026-08-16 05:45 UTCEG score recompute
  46. 2026-08-16 02:14 UTCEPSS rescore
  47. 2026-08-15 03:52 UTCEG score recompute
  48. 2026-08-15 01:30 UTCEPSS rescore
  49. 2026-08-14 01:59 UTCEG score recompute
  50. 2026-08-13 22:00 UTCEPSS rescore
  51. 2026-08-13 00:05 UTCEG score recompute
  52. 2026-08-12 13:51 UTCEPSS rescore
  53. 2026-08-11 22:12 UTCEG score recompute
  54. 2026-08-11 09:10 UTCEG score recompute
  55. 2026-08-11 00:00 UTCEPSS rescore
  56. 2026-08-09 18:19 UTCEG score recompute
  57. 2026-08-09 13:46 UTCEPSS rescore
  58. 2026-08-09 05:23 UTCEG score recompute
  59. 2026-08-08 16:37 UTCEPSS rescore
  60. 2026-08-08 03:29 UTCEG score recompute
  61. 2026-08-07 01:35 UTCEG score recompute
  62. 2026-08-06 13:47 UTCEPSS rescore
  63. 2026-08-05 23:42 UTCEG score recompute
  64. 2026-08-05 19:17 UTCEPSS rescore
  65. 2026-08-04 21:22 UTCEG score recompute
  66. 2026-08-04 15:10 UTCEPSS rescore
  67. 2026-08-04 10:39 UTCEPSS rescore
  68. 2026-08-03 18:19 UTCEG score recompute
  69. 2026-08-03 10:36 UTCEPSS rescore
  70. 2026-08-02 02:54 UTCEG score recompute
  71. 2026-08-02 02:27 UTCEPSS rescore
  72. 2026-08-01 13:57 UTCEG score recompute
  73. 2026-08-01 04:16 UTCEPSS rescore
  74. 2026-07-30 23:03 UTCEG score recompute
  75. 2026-07-30 16:28 UTCEPSS rescore

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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 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 0.5% probability of exploitation in the next 30 days (40th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-55213?
CVE-2026-55213 has a CVSS base score of 7.5 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-55213?
No fix for CVE-2026-55213 is confirmed yet. Until one is published, restrict network exposure of the affected system or apply the vendor's mitigation — for example, keep it off the internet or limit it to trusted networks — and watch the vendor's advisory for the fix.

Dependency Blast Radius

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