Craft is a content management system (CMS). The dataUrl function can be exploited if an attacker has write permissions on system notification templates. This function accepts an absolute file path, reads the file's content, and converts it into a Base64-encoded string. By embedding this function within a system notification template, the attacker can exfiltrate the Base64-encoded file content through a triggered system email notification. Once the email is received, the Base64 payload can be decoded, allowing the attacker to read arbitrary files on the server. This is fixed in 5.4.9 and 4.12.8.

Affected: Packagist: craftcms/cms

### Summary By abusing the mail notification template it is possible to read arbitrary operating system files.

### Details The [dataUrl](https://craftcms.com/docs/3.x/dev/functions.html#dataurl) function can be exploited if an attacker has write permissions on system notification templates. This function accepts an absolute file path, reads the file's content, and converts it into a Base64-encoded string. By embedding this function within a system notification template, the attacker can exfiltrate the Base64-encoded file content through a triggered system email notification. Once the email is received, the Base64 payload can be decoded, allowing the attacker to read arbitrary files on the server.

Requirements: * write permissions to system notification templates * ability to trigger a corresponding system email

### PoC 1) Modify a template to contain the following twig template string: ```twig {{ dataUrl('/var/www/web/.env') }} ``` 2) Trigger the corresponding notification email (e.g. by resetting a password) 3) Receive the email and decode the base64 string

Mail received: 

Decoded string: 

### Impact 1) Exposure of Sensitive Information: Arbitrary file read can lead to the exposure of sensitive data such as configuration files (…