TypiCMS Core has Stored Cross-Site Scripting (XSS) via SVG File Upload #### I. Summary A Stored Cross-Site Scripting (XSS) vulnerability exists in the file upload module of TypiCMS. The application allows users with file upload permissions to upload SVG files. While there is a MIME type validation, the content of the SVG file is not sanitized. An attacker can upload a specially crafted SVG file containing malicious JavaScript code. When another user (such as an administrator) views or accesses this file through the application, the script executes in their browser, leading to a compromise of that user's session. The issue is exacerbated by a bug in the SVG parsing logic, which can cause a 500 error if the uploaded SVG does not contain a `viewBox` attribute. However, this does not mitigate the XSS vulnerability, as an attacker can easily include a valid `viewBox` attribute in their malicious payload. #### II. Vulnerability Details * **Vulnerability Type:** Stored Cross-Site Scripting (XSS) (CWE-79) * **Affected Component:** `TypiCMS\Modules\Core\Http\Requests\FileFormRequest.php` and `TypiCMS\Modules\Core\Services\FileUploader.php`. * **Affected Versions:** <= 16.0.5 The vulnerability stems from two main points: 1. **Permissive File Validation:** The `FileFormRequest` explicitly whitelists `svg` as an allowed MIME type for uploads. 2. **Lack of Content Sanitization:** The `FileUploader` service saves the SVG file to the server without parsing and sanitizing its content to remove potentially malicious elements like ` If you see this, the script has run. ``` 2. **Upload the Malicious File:** * Log in to the TypiCMS admin panel as a user with permissions to upload files. * Navigate to the "Files" module (e.g., `/admin/files`). * Upload the `malicious.svg` file. The application will accept the file and store it.

3. **Trigger the XSS:** * The application will provide a public URL for the uploaded file, typically in the format `http:///storage/files/malicious.svg`. * Anyone who navigates to this URL will have the embedded JavaScript executed in their browser. * An attacker can send this link to a privileged user (e.g., an administrator). When the administrator clicks the link, their session cookies can be stolen, or the attacker can perform actions on their behalf.

#### IV. Impact Successful exploitation of this vulnerability allows an attacker to execute arbitrary JavaScript in the context of the victim's browser. Although the use of the `HttpOnly` flag on session cookies prevents direct theft of the session ID via `document.cookie`, the attacker can still achieve a full compromise of the victim's account by performing actions on their behalf. The impact includes: * **Account Takeover via Action Forgery:** The attacker's script can make authenticated requests to the application's API from the victim's browser. This allows the attacker to perform any action the victim is authorized to do, such as: * Creating a new administrator account for the attacker. * Changing the victim's email address and password. * Deleting or modifying all content, users, and settings. * **Sensitive Information Disclosure:** The script can read the content of any page the victim views within the admin panel. This includes lists of users (with names and emails), private application settings, and other sensitive data, which can then be exfiltrated to an attacker-controlled server. * **Phishing and Social Engineering:** The script can manipulate the admin panel's UI to display fake login forms to trick the user into re-entering their credentials, or redirect them to a malicious website. * **Keystroke Logging:** The script can capture any information the victim types into forms on the compromised page. Because the attacker can perform any action as an authenticated administrator, this vulnerability effectively leads to a **full application compromise**, even without direct access to the session cookie. The risk is **High**. #### V. Recommended Patches and Mitigations It is recommended to apply a defense-in-depth approach to mitigate this vulnerability. 1. **Primary Fix: Sanitize SVG Content:** The most robust solution is to sanitize SVG files upon upload. Before saving the file, it should be parsed to remove all potentially dangerous elements, including `

CVE-2026-27621 Blast Radius

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