CVE-2026-55559
A public proof of concept exists; no exploitation attested.
- Published2026-08-28
- Fixed in5.13.2 · 5.12.8
- WeaknessCWE-1336 · CWE-470 · CWE-94
Am I affected?
Debian, Ubuntu or Red Hat sometimes backport a fix without changing the upstream version number: such a version reads « to verify », never « affected ».With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.
Description
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.
Timeline
dates in UTC- 2026-08-2820:18CVE publishedNVD
Observed activity
isMalicious corpus · updated 2026-10-23 21:37 UTCBlock these indicators
- Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-55559?format=txt
- CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-55559?format=csv
- TAXII collection of exploited CVEs
- The EDL and CSV take an API key on the Pro plan.
Versions per branch
OSV| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 5.13 | ≥ 5.13.0, < 5.13.2 | 5.13.2 | OSV |
| 5.12 | < 5.12.8 | 5.12.8 | OSV |
as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.
Fix
- Update yamcs-core to 5.13.2 · 5.12.8
Detection
read 2026-10-23 19:25 UTC- Nuclei template
- none so far ProjectDiscovery
- Exploit-DB
- no entry Exploit-DB
Sources
- NVDCVE recordread 2026-10-23
- CISA-ADPSSVC decisionpoc2026-08-28
- OpenCVESSVC decisionpoc—
- CNACVSS 3.19.8read 2026-10-23
- CNAweakness (CWE)CWE-1336, CWE-470, CWE-94read 2026-10-23
- FIRST EPSSEPSS score0.8 %2026-10-22
- PoC-in-GitHubproof of concept1read 2026-10-23
- OSVaffected packages—
Technical details
- CVSS v3 Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Published
- 2026-08-28
- Last Modified
- 2026-09-08
- NVD status
- Awaiting Analysis
Frequently asked questions
What is CVE-2026-55559?
Is CVE-2026-55559 actively exploited?
What is the CVSS score for CVE-2026-55559?
Running yamcs-core? Hear about its next vulnerability
Surveillance reads the versions in your stack — a domain, a lockfile or a list — checks each CVE against the ranges its sources publish, and alerts you when one you run is exploited or enters CISA KEV. A version it cannot read stays « version not verified ».
No credit card required · No monthly cap on website lookups · 250 API requests/month
Go further
- Following what attackers exploit right now? The CISA KEV additions of the month, with their patch deadlines.
- Running this software? Vulnerability monitoring alerts you to new vulnerabilities in your products.
Related vulnerabilities
Same product first, then the same vendor advisory and the same publication week.