CVE-2026-55559
CriticalCVSS 9.8Summary
Yamcs prior to versions 5.12.8 and 5.13.2 inserts templateArgs from POST /api/instances and PATCH /api/instances/{instance} into YAML without YAML-context escaping. The rendered configuration is parsed by YamcsServer.createInstance and loaded by YamcsServerInstance, allowing an attacker to inject a services entry for org.yamcs.ProcessRunner. Successful exploitation executes commands as the Yamcs service account.
Risk Assessment
The risk includes arbitrary system command execution in the context of the service account, potentially leading to system and data integrity compromise.
Recommendation
It is recommended to immediately update Yamcs to versions 5.12.8 or 5.13.2, which contain the fix.
Original NVD description (English source)
Yamcs is a mission control framework. Prior to 5.12.8 and 5.13.2, Yamcs inserts templateArgs from POST /api/instances and PATCH /api/instances/{instance} into YAML through VarStatement.append in yamcs-core/src/main/java/org/yamcs/templating/VarStatement.java without YAML-context escaping. The rendered configuration is parsed by YamcsServer.createInstance and loaded by YamcsServerInstance, allowing an attacker to inject a services entry for org.yamcs.ProcessRunner. Deployments without security.yaml expose the operation through the guest superuser, while secured deployments require SystemPrivilege.CreateInstances. Successful exploitation executes commands as the Yamcs service account. This issue is fixed in versions 5.12.8 and 5.13.2.