CVE-2026-55559: Yamcs remote code execution via YAML injection in instance template

CVE-2026-55559 · Severity: critical · CVSS 9.8 · Published 2026-08-28

Yamcs, a spacecraft operations and telemetry system, allows unauthenticated users with no privileges (or users with the CreateInstances privilege) to execute arbitrary commands on the host server. An attacker can inject malicious YAML code through template arguments when creating or updating instances, which is then parsed and instantiated as a service, allowing execution of arbitrary processes with the privileges of the Yamcs service account. This includes access to secret keys, database credentials, and command/telemetry data for all instances on the server.

Technologies: org.yamcs:yamcs-core (Maven). Vendors: Maven.

Quick answers

Is CVE-2026-55559 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55559 being exploited in the wild.
How severe is CVE-2026-55559?
Critical severity, with a CVSS score of 9.8, published 28 August 2026.
Which products and versions are affected?
org.yamcs:yamcs-core (Maven) ECOSYSTEM:introduced=5.13.0,fixed=5.13.2.
Is there a fix for CVE-2026-55559?
Yes. org.yamcs:yamcs-core (Maven): upgrade to 5.13.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-55559 attacked?
It is attacked over the network, in a hosted service.
Am I affected by CVE-2026-55559?
Check whether you run org.yamcs:yamcs-core (Maven) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • org.yamcs:yamcs-core (Maven): upgrade to 5.13.2 or later
    # set org.yamcs:yamcs-core to 5.13.2 in your pom.xml or build.gradle

Technical details

The vulnerability is a YAML injection in the template processing engine (VarStatement.java). Template arguments (`templateArgs`) sent to POST `/api/instances` or PATCH `/api/instances/{instance}` are substituted into a template without escaping YAML-special characters (newlines, colons, quotes). The rendered config is then parsed as YAML and services are instantiated by class name via reflection. An attacker crafts a `templateArgs` value that closes an enclosing YAML string quote, injects a new `services:` entry pointing to `org.yamcs.ProcessRunner`, and comments out trailing syntax. The ProcessRunner executes arbitrary commands via `ProcessBuilder.start()`. The API endpoint requires the `CreateInstances` privilege, but by default (no `security.yaml`), the guest user is a superuser with unauthenticated API access. Attack vector is network; no user interaction required. Patched in versions 5.12.8 and 5.13.2.

Affected products

  • Yamcs yamcs-core 5.13.0 through 5.13.1; 5.12.7 and earlier

Identifiers

  • CVE-2026-55559
  • GHSA-73mf-m39p-wpm9

Timeline

  • 2026-08-28: disclosed: GHSA-73mf-m39p-wpm9 published
  • 2026-08-28: patched: Patched in versions 5.12.8 and 5.13.2

References

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