CVE-2021-48007 in PocketMine-MP
Summary
by MITRE • 09/06/2026
PocketMine-MP versions before 3.18.1 fail to validate NaN or INF values in MovePlayerPacket position and rotation fields. Malicious clients can send crafted movement packets with invalid floating-point values to crash servers through unhandled mathematical operations or prevent clients from rendering other players.
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Analysis
by VulDB Data Team • 09/06/2026
The vulnerability identified in PocketMine-MP versions prior to 3.18.1 represents a critical input validation failure within the server's handling of networked player movement data. Specifically, the MovePlayerPacket structure, which is responsible for transmitting positional and rotational coordinates between clients and the server during gameplay, lacks robust sanitization routines for floating-point values. This oversight allows malicious actors to inject non-standard IEEE 754 floating-point representations, namely Not-a-Number (NaN) and Infinity (INF), into the position and rotation fields of these packets. In standard software engineering practices, input validation is a fundamental defense layer designed to ensure that data received from external sources conforms to expected formats and ranges before being processed by core application logic. The absence of this check in PocketMine-MP exposes the server's internal mathematical engines to malformed inputs that deviate significantly from valid coordinate systems used for spatial calculations in 3D environments.
From a technical perspective, the exploitation of this flaw relies on the server's inability to gracefully handle or reject invalid floating-point arithmetic operations triggered by these crafted packets. When the server attempts to process NaN or INF values within its physics engine, rendering pipeline, or collision detection systems, it encounters undefined behavior typical of unhandled mathematical exceptions in many programming languages and runtime environments. For instance, performing any arithmetic operation with a NaN value typically results in another NaN, which can propagate through subsequent calculations, leading to logic errors that may cause the application state to become corrupted. Similarly, Infinity values can disrupt distance calculations or boundary checks, potentially causing infinite loops or memory access violations depending on how the underlying engine interprets these extremes. This lack of defensive programming allows a single malformed packet to destabilize the server process, often resulting in an immediate crash or termination of the main game loop due to uncaught exceptions thrown by the runtime environment when encountering illegal mathematical states.
The operational impact of this vulnerability is severe for both server stability and client-side user experience. On the server side, successful exploitation leads to a Denial of Service condition where the Minecraft Pocket Edition server becomes unavailable to all connected players until it is manually restarted. This disrupts gameplay continuity and requires administrative intervention to restore service, which can be particularly damaging in persistent multiplayer environments or competitive servers that rely on high availability. Furthermore, even if the server does not crash immediately due to specific engine optimizations or error handling mechanisms, the presence of NaN values in position data can cause rendering artifacts for other clients. Players may see avatars frozen at incorrect locations, flickering textures, or complete disappearance from their viewports because the client-side renderer cannot interpret invalid coordinate data correctly. This degrades the immersive experience and can be used to harass specific users by obscuring them from the game world without necessarily taking down the entire server infrastructure.
This vulnerability aligns with Common Weakness Enumeration (CWE) categories such as CWE-20 Improper Input Validation, which describes failures in checking or filtering input data before processing it, and CWE-754 Improper Check for Unusual or Exceptional Conditions, where software fails to handle unexpected but possible inputs like extreme floating-point values. In the context of the MITRE ATT&CK framework, this exploitation technique falls under T1498 Network Denial of Service, specifically involving resource exhaustion through application crashes caused by malformed network traffic. The attack vector is classified as remote with low complexity since it requires only sending a single crafted packet over the network protocol without needing prior authentication or complex setup procedures.
To mitigate this vulnerability, administrators must upgrade PocketMine-MP to version 3.18.1 or later, where developers have implemented strict validation checks for floating-point fields within the MovePlayerPacket handler. These updates ensure that any NaN or INF values are detected and rejected before they reach critical game logic modules. Additionally, server operators should enforce network-level filtering if possible, though application-layer fixes remain the primary defense. It is also advisable to monitor server logs for repeated connection attempts from suspicious sources sending malformed packets, as this may indicate active probing by attackers attempting to exploit similar weaknesses in other packet types or future unpatched versions of the software. Maintaining up-to-date software dependencies and applying security patches promptly are essential practices to prevent such input validation flaws from being leveraged against game infrastructure.