CVE-2026-55511: Yamcs vulnerable to authenticated RCE via StreamSQL aggregate-compiler column-name injection in Yamcs `executeSql`

An authenticated Yamcs user holding SystemPrivilege.ControlArchiving can cause Yamcs to compile attacker-controlled Java source through the StreamSQL aggregate expression compiler reachable from POST /api/archive/{instance}:executeSql.

The injected code executes inside the Yamcs server JVM with the privileges of the Yamcs server process, bypassing the Yamcs authorization model. Because this is ordinary Java execution, dangerous JDK APIs such as filesystem access, process execution, reflection, and class loading are reachable unless externally sandboxed. This allows compromise of confidentiality, integrity, and availability of the Yamcs deployment: access to mission data and credentials available to the process, telemetry/archive tampering, denial of service, and lateral movement from the host environment.

ControlArchiving is the archive/table/stream management privilege — distinct from both superuser access and the ChangeMissionDatabase privilege used by the previously fixed algorithm-override Janino issue (CVE-2026-44632). Scope is scored as Changed because execution crosses from an authenticated Yamcs API privilege into arbitrary code execution under the server process / host OS authority, outside the privileges granted to the authenticated Yamcs user (consistent with the maintainer’s S:C scoring of the sibling CVE-2026-44632).