# CVE-2026-27621: core XSS — Fixed in 16.1.7

🐘 Packagist

Not in CISA KEV

# CVE-2026-27621 — core

[Fix: TypiCMS/Core@d480a0b](https://github.com/TypiCMS/Core/commit/d480a0be1e8e7c0600bb9a325bb11920ee66497d)

CVE-2026-27621 is a Cross-site Scripting (XSS) vulnerability in typicms/core. A fix is available for typicms/core — see the affected versions and patch details below.

TypiCMS Core has Stored Cross-Site Scripting (XSS) via SVG File Upload

Also known as[GHSA-xfvg-8v67-j7wp](/vulnerability/GHSA-xfvg-8v67-j7wp)

Published

Feb 25, 2026

Updated

Oct 28, 2026

Affected

5 pkgs

Patched

5 / 5

Exploits

None indexed

Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

## Exploitation Status

### Proof-of-concept exploit code exists

-   CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-27621.

## EPSS Exploitation Probability

[via FIRST.org ↗](https://www.first.org/epss/)

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs13th percentile — riskier than 13% of all scored CVEsHighest risk

0.00%0.26%0.51%0.77%0.0%0.2%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from [FIRST.org EPSS](https://www.first.org/epss/).

## Real-World Exposure

5 pkgs affected

🐘`typicms/core`🐘`typicms/core`🐘`typicms/core`🐘`typicms/core`🐘`typicms/core`

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

## Description

#### 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 `<script>` tags or `on*` event handlers.

When the default filesystem disk is set to `public`, the uploaded SVG file is stored in a publicly accessible directory, making it trivial to access the file via a direct URL and trigger the XSS payload.

#### III. Proof of Concept (PoC)

1.  **Create a Malicious SVG File:** Create a file named `malicious.svg` with the following content. The `viewBox` attribute is included to bypass the application's parsing bug.
    
    ```
    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
        <script>
            // A simple PoC to demonstrate the vulnerability
            alert('XSS in TypiCMS! Your session cookie is: ' + document.cookie);
        </script>
        <text x="10" y="50">If you see this, the script has run.</text>
    </svg>
    ```
    
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. <img width="2540" height="1217" alt="image" src="https://github.com/user-attachments/assets/beb8ace9-ac39-442c-a2bc-3fbfb09f8c32" />

<img width="1718" height="671" alt="image" src="https://github.com/user-attachments/assets/9cd4a3f8-28e3-4223-8203-7ab292eaf95f" />

1.  **Trigger the XSS:**
    -   The application will provide a public URL for the uploaded file, typically in the format `http://<your-site>/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.

<img width="2091" height="704" alt="image" src="https://github.com/user-attachments/assets/99c915bb-a518-46aa-b237-390cd58f34e7" /> <img width="1457" height="996" alt="image" src="https://github.com/user-attachments/assets/0ed000ec-78cf-4ed8-8cd5-2886fbb2afc0" />

#### 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 `<script>`, `<style>`, `<foreignObject>` tags, and all `on*` event attributes. This can be achieved using a dedicated SVG sanitization library.
    
2.  **Secondary Fix: Disable SVG Uploads:** If SVG uploads are not a critical feature for the application, the simplest and most secure solution is to disable them entirely. This can be done by removing `'svg'` from the list of allowed MIME types in `TypiCMS\Modules\Core\Http\Requests\FileFormRequest.php`.
    
    ```
    // In FileFormRequest.php
    // BEFORE:
    $fileRule = 'mimes:jpeg,gif,png,...,svg,...|max:...';
    
    // AFTER:
    $fileRule = 'mimes:jpeg,gif,png,...,pdf,...|max:...'; // Removed 'svg'
    ```
    
3.  **Hardening - Content-Security-Policy (CSP):** Implement a strict Content-Security-Policy (CSP) header for the application. A well-configured CSP can prevent the execution of inline scripts, which would mitigate the impact of this XSS vulnerability.
    
4.  **Hardening - Serve User Content from a Separate Domain:** Serve all user-uploaded files from a separate, cookie-less domain. This is a highly effective security measure that isolates user-generated content from the main application, preventing scripts from accessing session cookies or interacting with the application's DOM.
    

## Affected Packages

5 total 5 fixed

Ecosystem

Package

Vulnerable range

Fix

🐘Packagist

`typicms/core` 

≥ 16.0.0&&< 16.1.7

16.1.7`composer require typicms/core:^16.1.7`

🐘Packagist

`typicms/core` 

≥ 15.0.0&&< 15.0.29

15.0.29`composer require typicms/core:^15.0.29`

🐘Packagist

`typicms/core` 

≥ 14.0.0&&< 14.0.27

14.0.27`composer require typicms/core:^14.0.27`

🐘Packagist

`typicms/core` 

≥ 13.0.0&&< 13.0.9

13.0.9`composer require typicms/core:^13.0.9`

🐘Packagist

`typicms/core` 

all versions

12.0.5`composer require typicms/core:^12.0.5`

## Affected Products

1 product · 1 configurations

Application

`typicms`typicms

< 16.1.7

range

## Detection & mitigation playbook

Open-source dependency

1.  ### Detect
    
    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for typicms/core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
    
2.  ### Fix
    
    Update typicms/core to 16.1.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27621 is resolved across your whole dependency graph.
    
3.  ### Workarounds
    
    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
    

## Frequently Asked Questions

\#### 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 pars

O3 Security · Impact-Aware SCA

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