Executive brief
PocketMine-MP is a server software for Minecraft Pocket Edition games. A vulnerability in the login packet handler allows remote attackers to send specially crafted login requests with excessive junk data, causing the server to waste CPU time logging warnings and degrading performance for legitimate players.
Technical details
The vulnerability is a denial-of-service condition in the LoginPacket handler where the JsonMapper instance processes the clientData JWT with a configuration that warns on unexpected properties instead of rejecting them. Remote attackers can craft malicious login packets containing large numbers of junk properties in the JWT body, causing the server to flood warning messages and waste CPU cycles. The attack requires network access to the server's login endpoint and no authentication. The fix, deployed in version 5.42.1, restricts unknown properties to a maximum of 10 and rejects packets exceeding this limit while maintaining compatibility with legitimate JWT variations from Microsoft.
Affected products
- PocketMine Project PocketMine-MP before 5.42.1
Timeline
- 2026-04-14: disclosed: GitHub security advisory GHSA-xp4f-g2cm-rhg7 published
- 2026-05-09: patched: Fix deployed in commit c1d4a81, version 5.42.1
- 2026-09-09: advisory: CVE-2026-86200 published