CVE-2021-39177

Name: CVE-2021-39177
Creator: NVD / NIST
Published: 2021-08-30T23:15:07.07+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 1.43%

Last modified Jun 17, 2026

CVE-2021-39177 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. 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. EPSS estimates a 1.43% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

1.43%

69.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-287

Affected Software

Vendor	Product	Versions
Geysermc	Geyser	< 1.4.2

References

https://github.com/GeyserMC/Geyser/commit/b9541505af68ac7b7c093206ac7b1ba88957a5a6Patch, Third Party Advisory
https://github.com/GeyserMC/Geyser/security/advisories/GHSA-h77f-xxx7-4858Patch, Third Party Advisory
https://updates.playhive.com/weekend-maintenance-disclosure-2kJMaYThird Party Advisory
https://github.com/GeyserMC/Geyser/commit/b9541505af68ac7b7c093206ac7b1ba88957a5a6Patch, Third Party Advisory
https://github.com/GeyserMC/Geyser/security/advisories/GHSA-h77f-xxx7-4858Patch, Third Party Advisory
https://updates.playhive.com/weekend-maintenance-disclosure-2kJMaYThird Party Advisory

Timeline

Published: Aug 30, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-39177?

How severe is CVE-2021-39177?

CVE-2021-39177 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 1.43% probability of exploitation in the next 30 days.

How do I fix CVE-2021-39177?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-39177?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST