{"id":"CVE-2026-78207","summary":"exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization","details":"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.","aliases":["GHSA-qwr4-7h29-chpf"],"modified":"2026-08-30T03:48:21.739501993Z","published":"2026-08-24T00:30:47.125Z","database_specific":{"cwe_ids":["CWE-1321"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/78xxx/CVE-2026-78207.json","cna_assigner":"VulnCheck"},"references":[{"type":"WEB","url":"https://www.npmjs.com/package/exceljs"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/78xxx/CVE-2026-78207.json"},{"type":"ADVISORY","url":"https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpf"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-78207"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serialization"},{"type":"PACKAGE","url":"https://github.com/exceljs/exceljs"},{"type":"ARTICLE","url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/exceljs/exceljs","events":[{"introduced":"0"},{"last_affected":"ac96f9a61e9799c7776bd940f05c4a51d7200209"}],"database_specific":{"source":"AFFECTED_FIELD","extracted_events":[{"introduced":"0"},{"last_affected":"4.4.0"}]}},{"type":"GIT","repo":"https://github.com/mateocallec/exceljs-hardened","events":[{"introduced":"0"},{"fixed":"37149551343c6305aa8aca4f43567c1091102287"}],"database_specific":{"extracted_events":[{"introduced":"0"},{"fixed":"5.0.0"}],"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"}}],"schema_version":"1.9.0","severity":[{"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"}]}