Critical 9.8Published Aug 28, 2026

CVE-2026-55559Yamcs: Remote Code Execution via instance-template argument YAML injection (createInstance)

Updated under an hour ago (2026-10-19 06:25 UTC)

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No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

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.

CVSS: 9.8 CRITICAL (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE): CWE-94, CWE-470, CWE-1336
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Awaiting Analysis
Record last updated: Aug 28, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

yamcs yamcs yamcs:yamcs (from the name)	before 5.12.8; from 5.13.0, < 5.13.2	CNA record

References

https://github.com/yamcs/yamcs/security/advisories/GHSA-73mf-m39p-wpm9x-refsource-confirm
https://github.com/yamcs/yamcs/commit/549f295cf8c5496a5e799d6bec2432ef976c82aax-refsource-misc
https://github.com/yamcs/yamcs/commit/7192da1c49bdf5ab1d72e579a47766a7c43e87c8x-refsource-misc
https://github.com/yamcs/yamcs/releases/tag/yamcs-5.12.8x-refsource-misc
https://github.com/yamcs/yamcs/releases/tag/yamcs-5.13.2x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.