CVE-2021-39177

User impersonation due to incorrect handling of the login JWT

Description

Geyser is a bridge between Minecraft: Bedrock Edition and Minecraft: Java Edition. Versions of Geyser prior to 1.4.2-SNAPSHOT allow anyone that can connect to the server to forge a LoginPacket with manipulated JWT token allowing impersonation as any user. Version 1.4.2-SNAPSHOT contains a patch for the issue. There are no known workarounds aside from upgrading.

Category

7.4
CVSS
Severity: High
CVSS 3.1 •
CVSS 2.0 •
EPSS 0.35%
Third-Party Advisory github.com Third-Party Advisory github.com Third-Party Advisory playhive.com
Affected: GeyserMC Geyser
Published at:
Updated at:

References

Link Tags
https://github.com/GeyserMC/Geyser/security/advisories/GHSA-h77f-xxx7-4858 third party advisory patch
https://github.com/GeyserMC/Geyser/commit/b9541505af68ac7b7c093206ac7b1ba88957a5a6 third party advisory patch
https://updates.playhive.com/weekend-maintenance-disclosure-2kJMaY third party advisory

Frequently Asked Questions

What is the severity of CVE-2021-39177?
CVE-2021-39177 has been scored as a high severity vulnerability.
How to fix CVE-2021-39177?
To fix CVE-2021-39177, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2021-39177 being actively exploited in the wild?
As for now, there are no information to confirm that CVE-2021-39177 is being actively exploited. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2021-39177?
CVE-2021-39177 affects GeyserMC Geyser.
This platform uses data from the NIST NVD, MITRE CVE, MITRE CWE, First.org and CISA KEV but is not endorsed or certified by these entities. CVE is a registred trademark of the MITRE Corporation and the authoritative source of CVE content is MITRE's CVE web site. CWE is a registred trademark of the MITRE Corporation and the authoritative source of CWE content is MITRE's CWE web site.
© 2025 Under My Watch. All Rights Reserved.