CVE-2026-54617 GravitLauncher CVE debrief

Who should care

Administrators and users of GravitLauncher, particularly those who have the LaunchServer file server exposed to untrusted networks, should assess their exposure and take immediate action to remediate the vulnerability.

Why it matters

CVE-2026-54617 is a critical vulnerability in GravitLauncher that allows an unauthenticated remote actor to potentially access sensitive files and credentials, enabling forged administrative access tokens and full authentication bypass. Immediate remediation is necessary to prevent exploitation.

• Potential exposure of signing keys, refresh-token material, and database credentials
• Possible forged administrative access tokens and full authentication bypass
• Potential for unauthorized access to sensitive files
• Need for immediate remediation to prevent exploitation

Technical summary

The vulnerability is caused by a lack of proper normalization and verification of the request-target in the FileServerHandler class. This allows an attacker to send a request with a leading slash stripped, potentially allowing them to access sensitive files. The affected product, GravitLauncher, is an open-source Minecraft launcher based on sashok724's v3. The vulnerability can be exploited by sending a raw HTTP request to the default LaunchServer file server on port 9274, allowing an unauthenticated remote actor to read any file accessible to the LaunchServer process, including sensitive files such as .keys/ecdsa_id, .keys/legacySalt, and LaunchServer.json. This can lead to exposure of signing keys, refresh-

Defensive priority

High priority for immediate remediation

Recommended defensive actions

• Immediately upgrade to version 5.7.12 or later
• Verify that the LaunchServer file server is not exposed to untrusted networks
• Monitor for suspicious activity on port 9274
• Consider implementing additional security measures such as authentication and authorization for the LaunchServer file server
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The vulnerability is caused by a lack of proper normalization and verification of the request-target in the FileServerHandler class. This allows an attacker to send a request with a leading slash stripped, potentially allowing them to access sensitive files.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.