Yamcs CVE-2026-55545

Asset / scope: Yamcs 5.12.7 WebSocket topics (packets, algorithm-status, mdb-changes)

Summary

Several WebSocket subscription handlers do not perform the privilege check that their REST counterparts enforce, so a principal subscribing over WebSocket receives data the REST API would have scoped or denied.

Root cause

• packets (PacketsApi.subscribePackets) performs no ReadPacket check, while the REST siblings do

(listPackets:128, streamPackets:256, subscribeContainers:538). A principal with a narrow ReadPacket scope receives the raw binary of all TM packets on the processor.

• algorithm-status (ProcessingApi.subscribeAlgorithmStatus) performs no check, while REST

getAlgorithmStatus enforces checkObjectPrivileges(ReadAlgorithm, ...) (:467).

• mdb-changes (MdbOverrideApi.subscribeMdbChanges) performs no check, while base MDB reads require

GetMissionDatabase.

Remediation

Bring each WebSocket subscription handler to parity with its REST sibling's privilege check (ReadPacket, ReadAlgorithm, GetMissionDatabase). This is the same declarative fail-closed fix as Report 1.

Supporting material

Subsystem source audit of the WS-vs-REST authorization parity. Available on request.

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Disclosure and credit

This was found by Cipher / Causal Security - https://causalsecurity.com/. We are coordinating disclosure via this report and request CVEs where you agree they qualify. We propose the 90-day window stated in your security policy. We might publish a write-up after a fix and the agreed window.