CVE-2021-39177

CVE-2021-39177 is a critical authentication bypass vulnerability affecting Geyser, a bridge between Minecraft: Bedrock Edition and Minecraft: Java Edition, specifically in versions prior to 1.4.2-SNAPSHOT. This flaw allows an unauthenticated attacker to forge a LoginPacket with a manipulated JWT token, enabling them to impersonate any user on the server. With a CVSS score of 9.8 (Critical), this vulnerability has a network attack vector, low attack complexity, and high impacts on confidentiality, integrity, and availability. There is no known active exploitation, publicly available exploit code, or significant community discussion surrounding this CVE.