CVE-2026-45289 Overview
CVE-2026-45289 is an authentication weakness in CloudburstMC Protocol, a protocol library for Minecraft Bedrock Edition. The library partially fails to validate FULL type authentication tokens within the EncryptionUtils methods used for auth payload verification. Servers depending on affected versions of the library can accept malformed or improperly signed authentication payloads. The flaw is classified under CWE-287: Improper Authentication. The maintainers released a fix in version 3.0.0.Beta12-20260420.182526-15. Publicly accessible Minecraft Bedrock servers built on the affected library are exposed to this issue over the network without user interaction.
Critical Impact
Attackers can reach the authentication validation path remotely without privileges, undermining the integrity of FULL type token verification on publicly exposed CloudburstMC Protocol deployments.
Affected Products
- CloudburstMC Protocol versions prior to 3.0.0.Beta12-20260420.182526-15
- Minecraft Bedrock Edition server software depending on the affected library
- Publicly accessible services using EncryptionUtils for FULL type token validation
Discovery Timeline
- 2026-06-02 - CVE-2026-45289 published to NVD
- 2026-06-02 - Last updated in NVD database
Technical Details for CVE-2026-45289
Vulnerability Analysis
The vulnerability resides in the CloudburstMC Protocol library, specifically within the EncryptionUtils class responsible for validating authentication payloads. The library supports multiple authentication token types, and the FULL type path lacks complete validation logic. As a result, the server-side trust decision about a connecting client's identity claims is made on partially verified data. The defect maps to CWE-287, improper authentication. The issue affects integrity of authentication state but does not expose confidential data or directly degrade availability based on the available scoring data.
Root Cause
The root cause is missing validation steps inside the EncryptionUtils methods that process FULL type authentication tokens. The verification routine does not enforce the full set of checks required to confirm the token's signature and claims chain. This permits crafted tokens to pass through portions of the validation pipeline that should reject them. The maintainers addressed the omission in version 3.0.0.Beta12-20260420.182526-15 by completing the validation logic. Refer to the GitHub Security Advisory GHSA-g2fr-c75x-4hf9 for technical details.
Attack Vector
The attack vector is network-based and requires no authentication or user interaction. A remote attacker connects to a publicly accessible Minecraft Bedrock server that uses an affected version of CloudburstMC Protocol. The attacker submits a crafted FULL type authentication payload that exploits the missing validation steps. Because no working proof-of-concept code is published in the advisory, exploitation specifics are described in prose only. Defenders should treat any unpatched, internet-facing CloudburstMC Protocol deployment as reachable by this class of attack.
Detection Methods for CVE-2026-45289
Indicators of Compromise
- Connection attempts presenting malformed or unexpected FULL type authentication tokens to CloudburstMC-based servers.
- Authentication events succeeding for clients whose token claims do not match the expected issuer chain.
- Unusual login patterns from anonymous sources against publicly exposed Bedrock servers running affected library versions.
Detection Strategies
- Inventory deployed CloudburstMC Protocol versions and flag any below 3.0.0.Beta12-20260420.182526-15.
- Inspect server logs for authentication events that bypass expected claim validation or originate from atypical client builds.
- Correlate inbound connection telemetry with successful sessions lacking a verified identity chain.
Monitoring Recommendations
- Forward Bedrock server authentication logs to a centralized logging or SIEM platform for anomaly review.
- Alert on spikes in failed-then-successful authentication sequences from the same source address.
- Monitor outbound activity from server hosts for signs of post-authentication abuse following unverified logins.
How to Mitigate CVE-2026-45289
Immediate Actions Required
- Upgrade CloudburstMC Protocol to version 3.0.0.Beta12-20260420.182526-15 or later across all dependent services.
- Identify any publicly accessible Bedrock servers built on the affected library and prioritize them for patching.
- Review authentication logs since deployment of the vulnerable versions for evidence of suspicious sessions.
Patch Information
The maintainers patched this issue in CloudburstMC Protocol version 3.0.0.Beta12-20260420.182526-15. The fix completes validation of FULL type authentication tokens within EncryptionUtils. Rebuild and redeploy any server software that pins or vendors the affected library. See the GitHub Security Advisory GHSA-g2fr-c75x-4hf9 for upgrade guidance.
Workarounds
- Restrict server exposure to trusted networks or known client allowlists until the upgrade is applied.
- Place affected Bedrock servers behind a reverse proxy or filtering layer that drops anomalous authentication payloads.
- Disable or limit acceptance of FULL type authentication tokens at the application layer if configuration permits, pending the patch.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
