How severe is CVE-2021-39177?

CVE-2021-39177 has a CVSS 3.x base score of 7.4, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2021-39177 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (70th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-39177?

CVE-2021-39177 affects Geysermc Geyser. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-39177?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-39177 published?

CVE-2021-39177 was published on 2021-08-30 and last updated on 2026-06-17.

CVE-2021-39177

CVE-2021-39177 is a high-severity vulnerability in Geysermc Geyser with a CVSS 3.x base score of 7.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-287.

Key facts

Severity: High (CVSS 3.x base score 7.4)
CVSS v2: 7.5
EPSS exploit prediction: 1% (70th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-287
Affected product: Geysermc Geyser
Published: 2021-08-30
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-39177?: 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.
How severe is CVE-2021-39177?: CVE-2021-39177 has a CVSS 3.x base score of 7.4, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2021-39177 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (70th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-39177?: CVE-2021-39177 affects Geysermc Geyser. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-39177?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-39177 published?: CVE-2021-39177 was published on 2021-08-30 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:geysermc:geyser:*:*:*:*:*:*:*:*

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