CVE-2021-39177 json
User impersonation due to incorrect handling of the login JWT
published 2021-08-30 5 y ago modified 2026-10-01 38 d ago also GHSA-h77f-xxx7-4858 , EUVD-2021-2067
- cvss
- 7.4
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 1.4%
- EPSS 1.4% chance of exploitation in 30 days, percentile 73%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- maven org.geysermc:connector 1.4.2-SNAPSHOT
- geysermc geyser 1.4.2
Exploit prediction
1.44% chance of exploitation in the next 30 days, higher than 73% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 7.4 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N |
| NVD | 3.1 | 9.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| NVD | 2.0 | 7.5 | AV:N/AC:L/Au:N/C:P/I:P/A:P |
| GitHub | 3.1 | 7.4 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| maven | org.geysermc:connector | <1.4.2-SNAPSHOT |
1.4.2-SNAPSHOT |
Affected products
- GeyserMC Geyser
Classification
- Weakness
-
- CWE-287 Improper Authentication
References
-
github.com
/GeyserMC/Geyser/commit/b9541505af68ac7b7c093206ac7b1ba88957a5a6
web, patch, third-party-advisory
-
github.com
/GeyserMC/Geyser/security/advisories/GHSA-h77f-xxx7-4858
web, patch, third-party-advisory
-
updates.playhive.com
/weekend-maintenance-disclosure-2kJMaY
third-party-advisory
-
nvd.nist.gov
/vuln/detail/CVE-2021-39177
advisory
-
github.com
/GeyserMC/Geyser
package
-
updates.playhive.com
/changelog/weekend-maintenance-breakdown
web
Sources
- CVE List CVE-2021-39177
- GitHub Advisory GHSA-h77f-xxx7-4858
- NVD CVE-2021-39177
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