exceljs exceljs-hardened prior 5.0.0 deepMerge prototype pollution

CVSS Meta Temp Score
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Current Exploit Price (≈)
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CTI Interest Score
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8.2$0-$5k0.41+

Summaryinfo

A vulnerability was found in exceljs exceljs-hardened. It has been rated as critical. This affects the function deepMerge. The manipulation leads to prototype pollution. This vulnerability is listed as CVE-2026-78207. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability was found in exceljs exceljs-hardened and classified as critical. This issue affects the function deepMerge. The manipulation with an unknown input leads to a prototype pollution vulnerability. Using CWE to declare the problem leads to CWE-1321. The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-78207 since 08/24/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1059 according to MITRE ATT&CK.

Upgrading to version 5.0.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-64682). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Vendor

Name

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔒
CNA CVSS-BT Score: 🔒
CNA Vector: 🔒

CVSSv3info

VulDB Meta Base Score: 8.3
VulDB Meta Temp Score: 8.2

VulDB Base Score: 7.3
VulDB Temp Score: 7.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 9.4
CNA Vector (VulnCheck): 🔒

CVSSv2info

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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Prototype pollution
CWE: CWE-1321 / CWE-94 / CWE-74
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: exceljs-hardened 5.0.0

Timelineinfo

08/24/2026 Advisory disclosed
08/24/2026 +0 days CVE reserved
08/24/2026 +0 days VulDB entry created
08/24/2026 +0 days VulDB entry last update

Sourcesinfo

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-78207 (🔒)
GCVE (CVE): GCVE-0-2026-78207
GCVE (VulDB): GCVE-100-394583
EUVD: 🔒

Entryinfo

Created: 08/24/2026 02:50
Updated: 08/24/2026 04:35
Changes: 08/24/2026 02:50 (38), 08/24/2026 02:51 (37), 08/24/2026 04:35 (1)
Complete: 🔍
Cache ID: 216::103

Be aware that VulDB is the high quality source for vulnerability data.

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