critical CVSS 9.1

CVE-2026-46621·Python vulnerability

Yamcs is a mission control framework. Prior to 5.12.7, the Yamcs script evaluation engine for Python algorithms dynamically compiled and evaluated user-controlled algorithm text using Jython through the JSR-223 ScriptEngine API without enforcing a secure sandbox, so an authenticated user with the ChangeMissionDatabase privilege could override an existing Python algorithm's logic through the mission database REST API and import and execute arbitrary Java classes such as java.lang.Runtime to achieve remote code execution on the underlying host operating system. This issue is fixed in versions 5.12.7 and 5.13.0, which disable algorithm editing by default.

Severity
critical
Software
Python
Fixed in
5.12.7
Published
2026-07-16

Affected versions

Until: 5.12.7

Fixed in: 5.12.7

How to fix this CVE

Update Yamcs to version 5.12.7 or later, which disables algorithm editing by default and removes the unsafe dynamic code evaluation vulnerability. If you are running Yamcs with the ChangeMissionDatabase privilege enabled, immediately restrict access to this privilege and audit recent algorithm modifications. After patching, verify that Python algorithm editing is disabled in your Yamcs configuration.

sudo dnf update yamcs yamcs-python3

Defensia detects this vulnerability

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Implement network-level restrictions on Yamcs REST API endpoints (/api/missionDatabase/algorithms) by requiring client certificate authentication, IP whitelisting, or rate-limiting PUT/POST requests to these endpoints. Additionally, enforce authentication token expiration and monitor for unusual algorithm modification activity patterns.

How to check if you are affected

  1. Run 'yamcs --version' or check /opt/yamcs/etc/version.txt to confirm the installed Yamcs version
  2. Query the Yamcs mission database REST API endpoint GET /api/missionDatabase/algorithms to list all Python algorithms and check modification timestamps against your change log
  3. Search Yamcs logs for patterns like 'algorithm.*updated' or 'ScriptEngine.*evaluate' with timestamps correlating to unauthorized changes
  4. Verify the fix by confirming that algorithm editing is disabled in yamcs.properties (look for 'algorithm.editing.enabled=false') and test that PUT requests to /api/missionDatabase/algorithms return 403 Forbidden

FAQ

What is CVE-2026-46621?

CVE-2026-46621 is a critical remote code execution vulnerability in Yamcs that allows authenticated users with ChangeMissionDatabase privilege to inject malicious Java code into Python algorithms via the REST API, bypassing sandboxing protections and gaining OS-level command execution.

Is CVE-2026-46621 being actively exploited?

No, this vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are currently available, though the attack requires only authenticated access with a specific privilege.

What versions of Yamcs are affected by CVE-2026-46621?

All Yamcs versions prior to 5.12.7 are vulnerable; versions 5.12.7 and 5.13.0 and later include the fix that disables algorithm editing by default.

How do I check if my server is vulnerable to CVE-2026-46621?

Run 'yamcs --version' to confirm you are running a version earlier than 5.12.7, then verify if algorithm editing is enabled by checking the yamcs.properties configuration file for 'algorithm.editing.enabled=true'.

Does Defensia detect CVE-2026-46621?

Yes — Defensia's CVE advisory scanner compares installed Yamcs package versions against the NVD database. If Yamcs is installed on a monitored server, CVE-2026-46621 will appear in your dashboard with remediation steps.

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References

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