Executive brief
CloudburstMC Protocol is a software library used by Minecraft Bedrock Edition servers to communicate with players. A security flaw in how the library handles login information could allow unauthorized users to bypass certain identity checks. This could potentially lead to players joining servers with incorrect or spoofed identity information, affecting the integrity of player data and server management.
Technical details
An improper authentication vulnerability (CWE-287) exists in CloudburstMC Protocol due to insufficient validation of 'FULL' type authentication tokens. The flaw is located within the EncryptionUtils methods responsible for validating authentication payloads, specifically failing to properly verify the 'xid' and 'xname' fields. A remote, unauthenticated attacker can exploit this over the network to submit crafted authentication payloads that bypass intended identity verification. This impacts software relying on this library, such as the Geyser proxy. The issue is resolved in version 3.0.0.Beta12-20260420.182526-15.
Affected products
- CloudburstMC Protocol < 3.0.0.Beta12-20260420.182526-15
Timeline
- 2026-05-12: advisory: GitHub Security Advisory published
- 2026-06-02: disclosed: NVD publication date