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.
CVE-2026-55559
CRITICALPre-NVD 9.89.8—
EchelonGraph scoreMEDIUM confidence
This critical-severity CVE scores 9.8 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.6%, top 56% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
Triggered by: NVD CVSS baseline
Sources: epss, secondary
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
- High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 9.8Exploit: None knownExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 9.8
- EG Score
- 9.8(medium)
- EG Risk
- 49(Track)EG Risk 49/100SSVC: Track
EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).
How it’s computedSeverity98% × 45%Exploitation1% × 40%Automatability30% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
- 1%
- EPSS %ILE
- 44%
- KEV
- Not listed
Published
August 28, 2026
Last Modified
August 28, 2026
Advisory Details (5)
Auto-updated Aug 28, 2026🔬 Proof of concept available. Patch available. Sources: github_commit, github_release, github.
github Patch Available🟡 PoC Available
Remote Code Execution via instance-template argument YAML injection (createInstance) · Advisory · yamcs/yamcs · GitHub
https://github.com/yamcs/yamcs/security/advisories/GHSA-73mf-m39p-wpm9github_release Patch Available
Yamcs 5.13.2
Patch available: yamcs/yamcs yamcs-5.13.2
https://github.com/yamcs/yamcs/releases/tag/yamcs-5.13.2github_release Patch Available
Yamcs 5.12.8
Patch available: yamcs/yamcs yamcs-5.12.8
https://github.com/yamcs/yamcs/releases/tag/yamcs-5.12.8github_commit
commit 7192da1c49bd (yamcs/yamcs)
Fix landed in yamcs/yamcs commit 7192da1c49bd — awaiting tagged release
https://github.com/yamcs/yamcs/commit/7192da1c49bdf5ab1d72e579a47766a7c43e87c8github_commit
commit 549f295cf8c5 (yamcs/yamcs)
Fix landed in yamcs/yamcs commit 549f295cf8c5 — awaiting tagged release
https://github.com/yamcs/yamcs/commit/549f295cf8c5496a5e799d6bec2432ef976c82aaVendor Advisories for CVE-2026-55559(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Weakness Classification(3)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 4× in last 7d / 4× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-08-30 02:52 UTCEG score recompute
- 2026-08-30 01:22 UTCEPSS rescore
- 2026-08-28 20:25 UTCEG score recompute
- 2026-08-28 18:10 UTCEG score recompute
Related CVEs(same CWE)
Same CWE
10 shownCWE-94
- CVE-2003-1432EG 10.0EPSS p94HIGH
- CVE-2002-0495EG 10.0EPSS p96HIGH
- CVE-1999-0702EG 10.0EPSS p98HIGH
- CVE-1999-0509EG 10.0EPSS p98HIGH
- CVE-2006-1318EG 9.3EPSS p97HIGH
- CVE-2006-1301EG 9.3EPSS p95HIGH
- CVE-2006-1308EG 9.3EPSS p95HIGH
- CVE-2006-1309EG 9.3EPSS p95HIGH
- CVE-2006-1304EG 9.3EPSS p96HIGH
- CVE-2006-1306EG 9.3EPSS p95HIGH
Frequently asked(5)
What is CVE-2026-55559?
CVE-2026-55559 is a critical vulnerability published on August 28, 2026. 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…
When was CVE-2026-55559 disclosed?
CVE-2026-55559 was first published in the National Vulnerability Database on August 28, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-55559 actively exploited?
CVE-2026-55559 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 56.3% of all scored CVEs.
What is the CVSS score of CVE-2026-55559?
CVE-2026-55559 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2026-55559?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-55559, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-55559
Is Your Infrastructure Affected by CVE-2026-55559?
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