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CVE-2026-78207— exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization

Quick assessment

Affected
exceljs exceljs
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 exceljs-hardened 5.0.0 版本之前，其 deepMerge 辅助函数中存在一个原型链污染漏洞。该漏洞在合并笔记对象时，未能正确拒绝 __proto__、constructor 或 prototype 等键。攻击者可以将包含恶意 __proto__ 属性的解析后的 JSON 数据赋值给单元格笔记，从而修改 Object.prototype，进而影响在此过程中创建的所有普通对象。

CVSS 9.4 · Critical
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I. Basic Information for CVE-2026-78207

Vulnerability Information
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Vulnerability Title
exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1321
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
exceljs exceljs 0 ~ 4.4.0 -

II. Public POCs for CVE-2026-78207

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 7598 chars
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III. Intelligence Information for CVE-2026-78207

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Other References for CVE-2026-78207 (3)

Same Patch Batch · exceljs · 2026-08-24 · 4 CVEs total

CVE-2026-78209 8.2 HIGH exceljs through 4.4.0 CSV Formula Injection via Unescaped Cell Values
CVE-2026-78206 7.5 HIGH exceljs through 4.4.0 Uncontrolled Resource Consumption via Unbounded xlsx Decompression
CVE-2026-78208 7.5 HIGH exceljs through 4.4.0 Path Traversal via Unvalidated addImage filename

IV. Related Vulnerabilities

Same product: exceljs
Same vendor: exceljs
Same weakness: CWE-1321

V. Comments for CVE-2026-78207

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