Critical
exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization
Type: advisorySources: OSV
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.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-78207
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 7 Nov 2026, 16:27 UTC · Revision 1
Source evidence
exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization
core-osv · Original sourcePublished 24 Aug 2026, 00:30 UTC
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.
osv:CVE-2026-78207
Complete source record
{
"id": "85abf6d32b49d8e90aa639ed1fcca6faf21e95cd45fdc6888d9886868b251359",
"url": "https://osv.dev/vulnerability/CVE-2026-78207",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization",
"summary": "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.",
"evidence": "osv:CVE-2026-78207",
"products": [],
"severity": "critical",
"structured": {
"id": "CVE-2026-78207",
"aliases": [
"CVE-2026-78207",
"GHSA-qwr4-7h29-chpf"
],
"metrics": [
{
"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"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/exceljs/exceljs",
"type": "GIT",
"events": [
{
"introduced": "0"
},
{
"last_affected": "ac96f9a61e9799c7776bd940f05c4a51d7200209"
}
],
"database_specific": {
"extracted_events": [
{
"range": [
{
"introduced": "0"
},
{
"last_affected": "4.4.0"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StandardRange"
},
{
"range": [
{
"introduced": "0"
},
{
"last_affected": "4.4.0"
}
],
"source": "DESCRIPTION"
}
]
}
}
],
"versions": [
"v4.4.0",
"v4.3.0",
"v4.2.1",
"v4.2.0",
"v4.1.1",
"v4.1.0",
"v4.0.1",
"v4.0.0",
"v3.10.0",
"v3.9.0",
"v3.8.2",
"v3.8.1",
"v3.8.0",
"v3.7.0",
"v3.5.0",
"v3.4.0",
"v3.3.1",
"v3.3.0",
"v3.2.0",
"v3.1.0",
"v3.0.0",
"v2.0.1",
"v2.0.0",
"v1.15.0",
"v1.14.0",
"v1.13.0",
"v1.12.2",
"v1.12.1",
"v1.12.0",
"v1.11.0",
"v1.10.0",
"v1.9.1",
"v1.9.0",
"v1.8.0",
"v1.7.0",
"v1.6.3",
"v1.6.2",
"v1.6.1",
"v1.6.0",
"v1.5.1",
"v1.5.0",
"v1.4.13",
"v1.4.12",
"v1.4.11",
"v1.4.10",
"v1.4.9",
"v1.4.8",
"v1.4.7",
"v1.4.6",
"v1.4.5",
"v1.4.4",
"v1.4.3",
"v1.3.0",
"v1.4.2",
"v1.4.1",
"v1.4.0",
"v1.2.1",
"v1.2.0",
"v1.1.3",
"v1.1.2",
"v1.1.1",
"v1.1.0",
"v1.0.2",
"v1.0.1",
"v1.0.0",
"v0.9.1",
"v0.9.0",
"v0.8.5",
"v0.8.4",
"v0.8.3",
"v0.8.2",
"v0.8.1",
"v0.8.0",
"v0.7.1",
"v0.7.0",
"v0.6.2",
"v0.5.1",
"v0.6.0",
"v0.5.0",
"v0.4.14",
"v0.4.13",
"v0.4.12",
"v0.4.11",
"v0.4.10",
"v0.4.9",
"v0.2.36",
"0.2.36",
"v0.2.35",
"0.2.35",
"v0.2.34",
"0.2.34",
"v0.2.33",
"0.2.33",
"v0.2.31",
"0.2.31",
"v0.2.30",
"0.2.30",
"v0.2.29",
"0.2.29",
"v0.2.28",
"0.2.28",
"v0.2.27",
"0.2.27",
"v0.2.26",
"0.2.26",
"v0.2.24",
"0.2.24",
"v0.2.23",
"0.2.23",
"v0.2.22",
"0.2.22",
"v0.2.21",
"0.2.21",
"v0.2.20",
"0.2.20",
"v0.2.19",
"0.2.19",
"v0.2.18",
"0.2.18",
"v0.2.17",
"0.2.17",
"v0.2.16",
"0.2.16",
"v0.2.15",
"0.2.15",
"v0.2.12",
"0.2.12",
"v0.2.11",
"0.2.11",
"v0.2.10",
"0.2.10",
"v0.2.8",
"0.2.8",
"v0.2.3",
"0.2.3",
"v0.2.2",
"v0.2.1",
"0.2.2",
"0.2.1",
"v0.2.0",
"0.2.0",
"v0.1.11",
"0.1.11",
"v0.1.10",
"0.1.10",
"v0.1.9",
"0.1.9",
"v0.1.8",
"0.1.8",
"v0.1.7",
"0.1.7",
"v0.1.6",
"0.1.6",
"v0.1.5",
"0.1.5",
"v0.1.4",
"0.1.4",
"v0.1.3",
"0.1.3",
"v0.1.2",
"0.1.2",
"v0.1.1",
"0.1.1",
"v0.1.0",
"0.1.0",
"v0.0.9",
"0.0.9",
"v0.0.8",
"0.0.8",
"v0.0.7",
"0.0.7",
"v0.0.6",
"0.0.6",
"v0.0.5",
"0.0.5",
"v0.0.4",
"0.0.4",
"v0.0.3",
"0.0.3",
"v0.0.2",
"0.0.2",
"v0.0.1",
"0.0.1"
],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-78207.json"
}
}
],
"modified": "2026-10-28T02:30:51.402418431Z",
"provider": "osv",
"references": [
"https://www.npmjs.com/package/exceljs",
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/78xxx/CVE-2026-78207.json",
"https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpf",
"https://nvd.nist.gov/vuln/detail/CVE-2026-78207",
"https://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serialization",
"https://github.com/exceljs/exceljs",
"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181"
],
"provider_metadata": {
"cwe_ids": [
"CWE-1321"
],
"cna_assigner": "VulnCheck",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/78xxx/CVE-2026-78207.json"
}
},
"related_cves": [
{
"value": "CVE-2026-78207",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 519865,
"published_at": "2026-08-24T00:30:47.125+00:00"
}