Critical severity · published Aug 30, 2021
CVE-2021-39177
Geyser is a bridge between Minecraft: Bedrock Edition and Minecraft: Java Edition
9.8
CVSS
1.4%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)1.4% · higher than 73% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
GE
Geyser · Geysermc
before 1.4.2 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-39177
CVE.org
https://www.cve.org/CVERecord?id=CVE-2021-39177
Patch
https://github.com/GeyserMC/Geyser/commit/b9541505af68ac7b7c093206ac7b1ba88957a5a6
Patch
https://github.com/GeyserMC/Geyser/security/advisories/GHSA-h77f-xxx7-4858
Third Party Advisory
https://updates.playhive.com/weekend-maintenance-disclosure-2kJMaY
More from Geyser
4.3
CVE-2026-42188
Geyser: Server-Side Request Forgery (SSRF) via Player Head Texture URL