CVE-2026-78207

CRITICALPre-NVD 9.49.4—
EchelonGraph scoreHIGH confidence

Score 9.4 from GitHub Security Advisory (severity: CRITICAL) published 2026-08-24. a secondary CVSS source baseline 9.4; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this week
9.4EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 9.4Exploit: None knownExposed: 0

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

exceljs through 4.4.0 contains a prototype pollution vulnerability in the deepMerge helper that fails to reject __proto__, constructor, or prototype keys when merging note objects. Attackers can assign parsed JSON with a malicious __proto__ property to cell notes, modifying Object.prototype and affecting all plain objects created in the process.

CVSS v3
9.4
EG Score
9.4(high)
EG Risk
57(Track)
EG Risk 57/100SSVC: 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
Severity94% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
38%
KEV
Not listed

Published

August 24, 2026

Last Modified

August 31, 2026

Advisory Details (4)

Auto-updated Sep 15, 2026
Patch available. Sources: github.
generic

exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization | Advisories | VulnCheck

https://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serialization
github Patch Available

Prototype Pollution in exceljs via `Note.model` / `_.deepMerge` · Advisory · mateocallec/exceljs-hardened · GitHub

https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpf
generic

exceljs/lib/utils/under-dash.js at v4.4.0 · exceljs/exceljs · GitHub

https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181
generic

GitHub - exceljs/exceljs: Excel Workbook Manager · GitHub

https://github.com/exceljs/exceljs

Vendor Advisories for CVE-2026-78207(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 50× in last 7d / 204× 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 204 total refreshes for this CVE.

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

Frequently asked(5)

What is CVE-2026-78207?
CVE-2026-78207 is a critical vulnerability published on August 24, 2026. exceljs through 4.4.0 contains a prototype pollution vulnerability in the deepMerge helper that fails to reject proto, constructor, or prototype keys when merging note objects. Attackers can assign parsed JSON with a malicious proto property to cell notes, modifying Object.prototype and affecting…
When was CVE-2026-78207 disclosed?
CVE-2026-78207 was first published in the National Vulnerability Database on August 24, 2026, with the most recent update on August 31, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-78207 actively exploited?
CVE-2026-78207 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 62.4% of all scored CVEs.
What is the CVSS score of CVE-2026-78207?
CVE-2026-78207 has a CVSS v3 base score of 9.4 (NVD).
How do I remediate CVE-2026-78207?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-78207, 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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