Answer in brief
CVE-2021-39177 records a High severity (CVSS 7.4) vulnerability in User impersonation due to incorrect handling of the login JWT. The current sources do not mark it as known exploited. The current feed maps org.geysermc:connector (maven). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.4. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps org.geysermc:connector (maven). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| org.geysermc:connectormaven | >=0 <1.4.2-SNAPSHOT | 1.4.2-SNAPSHOT |
Published upstream
Sep 7, 2021
Evidence: source:osv:source_dates:source-dates:recordSource modified
Sep 4, 2026
Evidence: source:osv:source_dates:source-dates:recordFirst seen by HOL
Aug 7, 2026
### Impact <!--_What kind of vulnerability is it? Who is impacted?_--> 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 <!--_Has the problem been patched? What versions should users upgrade to?_--> This was patched as part of https://github.com/GeyserMC/Geyser/commit/b9541505af68ac7b7c093206ac7b1ba88957a5a6 and https://github.com/GeyserMC/Geyser/commit/ab2f5b326fe590e09167e8b45b4b165ac06ecd13. if your Geyser version is `1.4.2-SNAPSHOT` or later, the issue has been addressed on your build. ### Workarounds <!--_Is there a way for users to fix or remediate the vulnerability without upgrading?_--> 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 <!--_Are there any links users can visit to find out more?_--> 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: * Come talk to us over on our [Discord](https://discord.gg/geysermc) server in the [#development](https://discord.com/channels/613163671870242838/613170125696270357) channel
Quoted source text, attributed separately from HOL analysis.