Executive brief
CefSharp.Common is a library used to embed web browsers into Windows applications. A security flaw in how it handles local file requests allows an attacker to potentially access sensitive files on the user's computer that should be restricted. This occurs when the application is configured to serve files from a specific folder but fails to properly verify that requested files are actually inside that folder.
Technical details
A path traversal vulnerability exists in CefSharp.Common's FolderSchemeHandlerFactory due to improper path validation. The component uses a raw string prefix check (StartsWith) on canonicalized paths to verify if a requested file resides within the configured root folder. Because it does not enforce a trailing directory separator, an attacker can use URL-encoded traversal sequences (e.g., ..%2f) to access sibling directories that share the same name prefix as the root folder (e.g., accessing 'www_secret' when the root is 'www'). Exploitation requires the attacker to influence the embedded browser to request a malicious URL handled by the affected scheme. The issue is resolved in version 148.0.90.
Affected products
- CefSharp CefSharp.Common < 148.0.90
Timeline
- 2026-05-29: disclosed: Initial disclosure to GitHub Advisory Database
- 2026-06-30: advisory: Advisory published and reviewed
- 2026-06-30: patched: Fix available in version 148.0.90