GHSA-m8vh-v6r6-w7p6

**Endpoint**: `admin/config/system` **Submenu**: `Languages` **Parameter**: `Supported` **Application**: Grav v 1.7.48

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## Summary

A Denial of Service (DoS) vulnerability was identified in the **"Languages"** submenu of the Grav **admin configuration panel** (`/admin/config/system`). Specifically, the `Supported` parameter fails to properly validate user input. If a malformed value is inserted—such as a single forward slash (`/`) or an XSS test string—it causes a fatal regular expression parsing error on the server.

This leads to application-wide failure due to the use of the `preg_match()` function with an **improperly constructed regular expression**, resulting in the following error:

`preg_match(): Unknown modifier 'o' File: /system/src/Grav/Common/Language/Language.php line 244`

Once triggered, the site becomes completely unavailable to all users.

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## Details

- **Vulnerable Endpoint**: `POST /admin/config/system` - **Submenu**: `Languages` - **Parameter**: `Supported`

The application dynamically constructs a regular expression using the contents of the `Supported` field without escaping the input using `preg_quote()` or proper validation. This allows attackers to inject invalid syntax into the regex engine, crashing the application during language resolution.

**Stack trace excerpt**:

`Whoops \ Exception \ ErrorException (E_WARNING) preg_match(): Unknown modifier 'o' /system/src/Grav/Common/Language/Language.php244`

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## Proof of Concept (PoC)

### Payloads:

`/ `

### Steps to Reproduce:

1. Log into the Grav Admin Panel. 2. Navigate to: **Configuration** → **System** → **Languages**. 3. Locate the `Supported` field. 4. Insert one of the payloads above (e.g., a single slash `/`). 5. Click **Save**.

<img width="1897" height="639" alt="Pasted image 20250719183223" src="https://github.com/user-attachments/assets/d3a54a20-d30d-46c6-9015-722f80701cfb" />

1. Observe: All pages in the application begin throwing a fatal error and become inaccessible.

<img width="1802" height="998" alt="Pasted image 20250719175229" src="https://github.com/user-attachments/assets/b16750c2-507f-4c30-a9bb-d07fa92bb777" />

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## Impact

- Application-wide Denial of Service (DoS) - All login and admin views crash with the same error - Potentially exploitable by: - Admin panel users - CSRF if misconfigured

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## References

- **CWE-1333**: Improper Regular Expression - **CWE-20**: Improper Input Validation

## Discoverer

[Marcelo Queiroz](www.linkedin.com/in/marceloqueirozjr)

by [CVE-Hunters](https://github.com/Sec-Dojo-Cyber-House/cve-hunters)