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CVE-2025-27800: Stored Cross-Site Scripting in Episerver Content Management System (CMS) Admin Dashboard

• Severity: medium (CVSS 4.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-07-28 · updated 2026-06-17
• Weakness: CWE-79

Description

The Episerver Content Management System (CMS) by Optimizely was affected by multiple Stored Cross-Site Scripting (XSS) vulnerabilities. This allowed an authenticated attacker to execute malicious JavaScript code in the victim's browser. The Admin dashboard offered the functionality to add gadgets to the dashboard. This included the "Notes" gadget. An authenticated attacker with the corresponding access rights (such as "WebAdmin") that was impersonating the victim could insert malicious JavaScript code in these notes that would be executed if the victim visited the dashboard. Affected products: Version 11.X: EPiServer.CMS.Core (<11.21.4) with EPiServer.CMS.UI (<11.37.5), Version 12.X: EPiServer.CMS.Core (<12.22.1) with EPiServer.CMS.UI (<11.37.3)

Affected products

• Optimizely Episerver Content Management System (CMS): from 11.x before 11.21.4; from 12.x before 12.22.1 — fixed in 11.21.4, 12.22.1

How to fix

Upgrade to a fixed version: Optimizely Episerver Content Management System (CMS) 11.21.4, 12.22.1. Check the vendor advisory for mitigations.

References

• https://api.nuget.optimizely.com/packages/episerver.cms.core/11.21.4#
• https://api.nuget.optimizely.com/packages/episerver.cms.core/12.22.1#
• https://r.sec-consult.com/optimizely
• http://seclists.org/fulldisclosure/2025/Aug/18

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