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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.

exceljs是exceljs组织的一款读取和写入Excel文件的JavaScript库。 exceljs 5.0.0之前版本存在输入验证错误漏洞，该漏洞源于deepMerge辅助程序在合并note对象时未拒绝__proto__、constructor或prototype键，导致原型污染，攻击者可将含恶意__proto__属性的解析JSON赋值给单元格注释，进而修改Object.prototype并影响进程中创建的所有普通对象。

CVSS 9.4 · Critical EPSS 0.60% · P48

Affected Version Matrix 1

VendorProduct Version RangeStatus
exceljs exceljs ≤ 4.4.0 affected
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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 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.
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
Vulnerability Title
exceljs 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
exceljs是exceljs组织的一款读取和写入Excel文件的JavaScript库。 exceljs 5.0.0之前版本存在输入验证错误漏洞，该漏洞源于deepMerge辅助程序在合并note对象时未拒绝__proto__、constructor或prototype键，导致原型污染，攻击者可将含恶意__proto__属性的解析JSON赋值给单元格注释，进而修改Object.prototype并影响进程中创建的所有普通对象。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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
AI-Generated POC Verified env Premium
Reproduced successfully in a real sandbox · Below is the actual recording of building the environment and exploiting the vulnerability.
Success marker: VULNERABLE: Object.prototype polluted — new {} inherited polluted="PROOF_fd90cd7be7b12b81" (proof token exfiltrated through exploit)
Reproduction recording is a Pro+ exclusive
Watch the full sandbox build + live exploit recording for this CVE. Limited-time ¥499/mo.
Upgrade to Pro+
claude_code · 7598 chars
GitHub 复现环境（可 clone 直接跑）
Pro+ exclusive includes:
Vulnerability reproduction recording (real sandbox build + trigger, exclusive)
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III. Intelligence Information for CVE-2026-78207

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Patches & Fixes for CVE-2026-78207 (1)

Vendor Advisories for CVE-2026-78207 (2)

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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