{
"id": "GHSA-3cpv-r8x3-29fp",
"aliases": [
"CVE-2026-78207"
],
"details": "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.",
"affected": [],
"modified": "2026-08-24T03:31:06Z",
"severity": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L"
},
{
"type": "CVSS_V4",
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
}
],
"published": "2026-08-24T03:31:06Z",
"references": [
{
"url": "https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpf",
"type": "WEB"
},
{
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-78207",
"type": "ADVISORY"
},
{
"url": "https://github.com/exceljs/exceljs",
"type": "WEB"
},
{
"url": "https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181",
"type": "WEB"
},
{
"url": "https://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serialization",
"type": "WEB"
}
],
"schema_version": "1.4.0",
"database_specific": {
"cwe_ids": [
"CWE-1321"
],
"severity": "CRITICAL",
"github_reviewed": false,
"nvd_published_at": "2026-08-24T01:16:58Z",
"github_reviewed_at": null
}
}