No exploitation reportedFix available

CVE-2021-39177

Q: Is CVE-2021-39177 actively exploited?

Active exploitation of CVE-2021-39177 has not been confirmed. Its EPSS score was 1.4% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-39177?

CVE-2021-39177 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

No exploitation reported by the sources we read.

Published2021-08-30
Fixed in1.4.2
WeaknessCWE-287

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC

2021-08-3023:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-39177?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-39177?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Geysermc geyser

Branch	Affected	Fixed in	Source
1.4	< 1.4.2	1.4.2	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Update Geysermc geyser to 1.4.2

Advisories and patches

github.comPatch
github.comPatch

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CNACVSS 3.17.4read 2026-10-23
NVDCVSS 3.19.8read 2026-10-23
NVDCVSS 2.07.5read 2026-10-23
CNAweakness (CWE)CWE-287read 2026-10-23
FIRST EPSSEPSS score1.4 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published: 2021-08-30
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-39177?

Is CVE-2021-39177 actively exploited?

Active exploitation of CVE-2021-39177 has not been confirmed. Its EPSS score was 1.4% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-39177?

CVE-2021-39177 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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