CVE-2026-97151: Mwilliamson Mammoth.js

High severity, CVSS 8.4. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• Mwilliamson Mammoth.js: before 1.12.2 (fixed in 1.12.2)

Published 2026-09-24. Last modified 2026-09-24.