---
id: CVE-2026-97151
title: >-
  mammoth (aka mammoth.js) before 1.12.2 is vulnerable to prototype pollution
  when reading the styles defined in a document
summary: >-
  mammoth (aka mammoth.js) before 1.12.2 is vulnerable to prototype pollution
  when reading the styles defined in a document. Converting a crafted .docx file
  allows an attacker to add arbitrary properties to Object.prototype. In 1.11.0
  thro…
severity: high
cvss: 8.4
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:L/VA:H/SC:N/SI:N/SA:N'
cwe:
  - CWE-1321
vendor: mwilliamson
product: mammoth
affected:
  - mammoth < 1.12.2
published: '2026-09-24'
updated: '2026-09-24'
sourceUpdated: '2026-09-24T04:18:06.027'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-97151'
references:
  - url: >-
      https://github.com/mwilliamson/mammoth.js/commit/2888fa158d67c1419199f152326e12a05618b53e
    label: cve@mitre.org
  - url: >-
      https://github.com/mwilliamson/mammoth.js/commit/31f0c370be4b95ac4fa285fea3be970606735f16
    label: cve@mitre.org
  - url: 'https://raw.githubusercontent.com/mwilliamson/mammoth.js/master/NEWS'
    label: cve@mitre.org
  - url: 'https://www.npmjs.com/package/mammoth'
    label: cve@mitre.org
tags:
  - nvd
  - cve.org
cvssSource: cna
ingestedAt: '2026-09-24T03:37:24.190Z'
---

## Overview

mammoth (aka mammoth.js) before 1.12.2 is vulnerable to prototype pollution when reading the styles defined in a document. Converting a crafted .docx file allows an attacker to add arbitrary properties to Object.prototype. In 1.11.0 through 1.12.1, applications that convert further documents in the same process and return the converted HTML can also disclose the contents of local server files (to the party supplying the documents) by setting externalFileAccess to true.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.