{"id":"CVE-2026-78207","aliases":["EUVD-2026-64682","GHSA-3cpv-r8x3-29fp","GHSA-qwr4-7h29-chpf"],"status":"published","title":"exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization","description":"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.","severity":{"version":"4.0","score":9.3,"vector":"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","level":"critical","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00603,"percentile":0.4919,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-1321"],"published":"2026-08-24T00:30:47Z","modified":"2026-11-08T14:09:03Z","products":[{"vendor":"exceljs","product":"exceljs"},{"vendor":"https://github.com/guyonroche","product":"exceljs"}],"references":[{"url":"https://github.com/exceljs/exceljs","tags":["product","package"]},{"url":"https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpf","tags":["third-party-advisory","vendor-advisory","advisory"]},{"url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181","tags":["technical-description","article"]},{"url":"https://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serialization","tags":["third-party-advisory","advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-78207","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-3cpv-r8x3-29fp"},{"url":"https://www.npmjs.com/package/exceljs","tags":["web"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/78xxx/CVE-2026-78207.json","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2026-78207","title":"exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization","description":"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.","status":"published","published":"2026-08-24T00:30:47.125Z","modified":"2026-11-08T14:09:03.861Z","cvss":[{"version":"4.0","score":9.3,"vector":"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","level":"critical","assessor":"cna"},{"version":"3.1","score":9.4,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L","level":"critical","assessor":"cna"}],"cwes":["CWE-1321"],"updated_at":"2026-11-08T15:43:34.234229Z"}],"euvd":[{"id":"EUVD-2026-64682","description":"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.","status":"published","published":"2026-08-24T00:30:47Z","modified":"2026-11-08T14:09:03Z","cvss":[{"version":"4.0","score":9.3,"vector":"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","level":"critical"}],"updated_at":"2026-11-08T15:13:06.469155Z"}],"ghsa":[{"id":"GHSA-3cpv-r8x3-29fp","title":"exceljs-hardened before 5.0.0 contains a prototype pollution vulnerability in the deepMerge...","description":"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.","status":"published","published":"2026-08-24T03:31:06Z","modified":"2026-08-24T03:31:14Z","cvss":[{"version":"4.0","score":9.3,"vector":"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","level":"critical"},{"version":"3.1","score":9.4,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L","level":"critical"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T15:10:52.810585Z"}],"nvd":[{"id":"CVE-2026-78207","description":"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.","status":"published","published":"2026-08-24T01:16:58.137Z","modified":"2026-10-14T13:10:00.187Z","cvss":[{"version":"4.0","score":9.3,"vector":"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","level":"critical","assessor":"secondary"},{"version":"3.1","score":9.4,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L","level":"critical","assessor":"secondary"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T14:12:41.018848Z"}],"osv":[{"id":"CVE-2026-78207","title":"exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization","description":"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.","status":"published","published":"2026-08-24T00:30:47.125Z","modified":"2026-11-09T02:31:08.718610321Z","cvss":[{"version":"4.0","score":9.3,"vector":"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","level":"critical"}],"cwes":["CWE-1321"],"updated_at":"2026-11-09T03:16:44.651171Z"}]}}