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 — 4 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-hardened before 5.0.0 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
37%
KEV
Not listed

Published

August 24, 2026

Last Modified

August 24, 2026

Advisory Details (4)

Auto-updated Aug 25, 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 27× in last 7d / 27× 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. 2026-08-26 16:24 UTCEG score recompute
  2. 2026-08-26 16:24 UTCGHSA enrichment
  3. 2026-08-26 14:47 UTCEPSS rescore
  4. 2026-08-26 12:09 UTCGHSA enrichment
  5. 2026-08-26 07:58 UTCGHSA enrichment
  6. 2026-08-26 03:47 UTCGHSA enrichment
  7. 2026-08-25 23:37 UTCGHSA enrichment
  8. 2026-08-25 19:26 UTCGHSA enrichment
  9. 2026-08-25 15:16 UTCEG score recompute
  10. 2026-08-25 15:16 UTCGHSA enrichment
  11. 2026-08-25 13:49 UTCEPSS rescore
  12. 2026-08-25 11:05 UTCGHSA enrichment
  13. 2026-08-25 06:55 UTCGHSA enrichment
  14. 2026-08-25 02:44 UTCGHSA enrichment
  15. 2026-08-24 22:34 UTCGHSA enrichment
  16. 2026-08-24 18:24 UTCEG score recompute
  17. 2026-08-24 18:24 UTCGHSA enrichment
  18. 2026-08-24 17:51 UTCEG score recompute
  19. 2026-08-24 17:51 UTCGHSA enrichment
  20. 2026-08-24 14:18 UTCEPSS rescore
  21. 2026-08-24 14:11 UTCGHSA enrichment
  22. 2026-08-24 10:01 UTCGHSA enrichment
  23. 2026-08-24 05:50 UTCEG score recompute
  24. 2026-08-24 05:50 UTCGHSA enrichment
  25. 2026-08-24 01:38 UTCEG score recompute
Show 2 more
  1. 2026-08-24 00:36 UTCEG score recompute
  2. 2026-08-24 00:35 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-78207?
CVE-2026-78207 is a critical vulnerability published on August 24, 2026. exceljs-hardened before 5.0.0 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…
When was CVE-2026-78207 disclosed?
CVE-2026-78207 was first published in the National Vulnerability Database on August 24, 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 63.5% 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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