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User impersonation due to incorrect handling of the login JWT

High severity GitHub Reviewed Published Aug 30, 2021 in GeyserMC/Geyser • Updated Feb 1, 2023

Package

maven org.geysermc:connector (Maven)

Affected versions

<= 1.4.1-SNAPSHOT

Patched versions

1.4.2-SNAPSHOT

Description

Impact

This allows anyone that can connect to the server to forge a LoginPacket with manipulated JWT token allowing impersonation as any Bedrock user. Unless credentials are saved in your configuration, online mode is not affected as users are still required to log in separately. If your credentials are saved, there is no risk of exposing your email or password.

Patches

This was patched as part of GeyserMC/Geyser@b954150 and GeyserMC/Geyser@ab2f5b3. if your Geyser version is 1.4.2-SNAPSHOT or later, the issue has been addressed on your build.

Workarounds

Geyser strongly recommends updating to fix this issue. If this isn't possible:

  • Use online mode and don't save credentials in your Geyser configuration
  • Use an additional authentication method on the Java server

References

This was disclosed to us by a staff member over at Hive; you can read their disclosure here: https://updates.playhive.com/weekend-maintenance-disclosure-2kJMaY

For more information

If you have any questions or comments about this advisory:

References

@Camotoy Camotoy published to GeyserMC/Geyser Aug 30, 2021
Published by the National Vulnerability Database Aug 30, 2021
Reviewed Sep 7, 2021
Published to the GitHub Advisory Database Sep 7, 2021
Last updated Feb 1, 2023

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS score

0.245%
(65th percentile)

Weaknesses

CVE ID

CVE-2021-39177

GHSA ID

GHSA-h77f-xxx7-4858

Source code

Credits

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