CVE-2026-55559

CRITICALPre-NVD 9.89.8
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

This critical-severity CVE scores 9.8 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.8% (54th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from a secondary CVSS source
Sources: EPSS, a secondary CVSS source
Elevated
9.8EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
CISA-KEV: Not listedEPSS PROB: 0.8%CVSS: 9.8Exploit: No code on recordExposed services: Not assessed

A fix is available — apply it.

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 v3
9.8
EG Score
9.8CRITICALmedium confidence
EG Risk
75
EG Risk 75/100

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 computed (value × EchelonGraph’s weight)
Severity98% × 45%
The EG Score, 9.8 of 10.
Exploitation40% × 40%
EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.
Automatability100% × 15%
CISA's SSVC Automatable value: yes (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low, Track* at medium and Attend at high mission impact.
Exploitation public PoC (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.8%
EPSS %ILE
54th
KEV
Not listed

SSVC (CISA's decision table, applied by EchelonGraph)Track at low, Track* at medium and Attend at high mission impact.

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation public PoC (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)3 days if the affected system is publicly exposed; 60 days if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

August 28, 2026

Last Modified

September 8, 2026

Advisory Details (5)

Auto-updated Oct 14, 2026
🔬 Proof of concept available. Patch available. Sources: github, github_commit, github_release.
GitHub advisoryMentions a patch (unverified)🟡 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-wpm9
GitHub release Patch Available

Yamcs 5.13.2

Patch available: yamcs/yamcs yamcs-5.13.2

https://github.com/yamcs/yamcs/releases/tag/yamcs-5.13.2
GitHub release Patch Available

Yamcs 5.12.8

Patch available: yamcs/yamcs yamcs-5.12.8

https://github.com/yamcs/yamcs/releases/tag/yamcs-5.12.8
GitHub commit

commit 7192da1c49bd (yamcs/yamcs)

Fix landed in yamcs/yamcs commit 7192da1c49bd — awaiting tagged release

https://github.com/yamcs/yamcs/commit/7192da1c49bdf5ab1d72e579a47766a7c43e87c8
GitHub commit

commit 549f295cf8c5 (yamcs/yamcs)

Fix landed in yamcs/yamcs commit 549f295cf8c5 — awaiting tagged release

https://github.com/yamcs/yamcs/commit/549f295cf8c5496a5e799d6bec2432ef976c82aa

Vendor 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.

Affected Packages

(1 across 1 ecosystem)
Maven(1)
PackageVulnerable rangeFix by version rangeDependents
org.yamcs:yamcs-core0.29.3 ... 5.9.9 (166 versions)
  • 5.13.0 up to 5.13.2: fixed in 5.13.2
  • every version up to 5.12.8: fixed in 5.12.8
—

Weakness Classification(3)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 15× in last 7d / 58× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

  1. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  2. 2026-10-13 14:21 UTCEG score recompute
  3. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  4. 2026-10-12 15:32 UTCEG score recompute
  5. 2026-10-11 19:39 UTCEG score recompute
  6. 2026-10-11 16:54 UTCEG score recompute
  7. 2026-10-11 14:17 UTCEG score recompute
  8. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  9. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  10. 2026-10-10 00:50 UTCEG score recompute
  11. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  12. 2026-10-09 02:39 UTCEG score recompute
  13. 2026-10-08 17:12 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  14. 2026-10-08 00:51 UTCEG score recompute
  15. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  16. 2026-10-06 15:55 UTCEG score recompute
  17. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  18. 2026-10-05 20:48 UTCEG score recompute
  19. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  20. 2026-10-04 23:36 UTCEG score recompute
  21. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  22. 2026-10-03 17:37 UTCEG score recompute
  23. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  24. 2026-10-02 18:50 UTCEG score recompute
  25. 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.8% · 54th percentile
Show 63 more
  1. 2026-10-02 00:37 UTCEG score recompute
  2. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  3. 2026-09-30 19:49 UTCEG score recompute
  4. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  5. 2026-09-30 03:49 UTCEG score recompute
  6. 2026-09-29 15:22 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  7. 2026-09-29 01:17 UTCEG score recompute
  8. 2026-09-28 14:20 UTCEG score recompute
  9. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  10. 2026-09-27 14:23 UTCEG score recompute
  11. 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  12. 2026-09-26 20:24 UTCEG score recompute
  13. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  14. 2026-09-26 08:04 UTCEG score recompute
  15. 2026-09-24 15:54 UTCEG score recompute
  16. 2026-09-24 14:04 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  17. 2026-09-23 19:52 UTCEG score recompute
  18. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.6% · 45th percentile
  19. 2026-09-22 18:17 UTCEG score recompute
  20. 2026-09-21 22:13 UTCEG score recompute
  21. 2026-09-20 22:15 UTCEG score recompute
  22. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  23. 2026-09-19 18:13 UTCEG score recompute
  24. 2026-09-18 21:28 UTCEG score recompute
  25. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  26. 2026-09-17 20:50 UTCEG score recompute
  27. 2026-09-17 19:31 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  28. 2026-09-16 18:58 UTCEG score recompute
  29. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  30. 2026-09-16 09:11 UTCEG score recompute
  31. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  32. 2026-09-15 04:10 UTCEG score recompute
  33. 2026-09-15 03:11 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  34. 2026-09-13 20:10 UTCEG score recompute
  35. 2026-09-13 16:47 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  36. 2026-09-12 16:11 UTCEG score recompute
  37. 2026-09-11 16:09 UTCEG score recompute
  38. 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  39. 2026-09-11 11:58 UTCEG score recompute
  40. 2026-09-10 11:53 UTCEG score recompute
  41. 2026-09-10 09:35 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  42. 2026-09-09 01:10 UTCEG score recompute
  43. 2026-09-08 22:01 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  44. 2026-09-07 19:01 UTCEG score recompute
  45. 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  46. 2026-09-06 16:32 UTCEG score recompute
  47. 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  48. 2026-09-05 16:34 UTCEG score recompute
  49. 2026-09-04 16:33 UTCEG score recompute
  50. 2026-09-04 08:32 UTCEG score recompute
  51. 2026-09-04 05:06 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  52. 2026-09-02 15:11 UTCEG score recompute
  53. 2026-09-02 14:12 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  54. 2026-09-01 15:04 UTCEG score recompute
  55. 2026-09-01 13:54 UTCEPSS rescoreEPSS 0.6% · 43rd percentile
  56. 2026-09-01 07:01 UTCEG score recompute
  57. 2026-09-01 04:40 UTCEPSS rescoreEPSS 0.6% · 43rd percentile
  58. 2026-08-30 22:52 UTCEG score recompute
  59. 2026-08-30 19:17 UTCEPSS rescoreEPSS 0.6% · 43rd percentile
  60. 2026-08-30 02:52 UTCEG score recompute
  61. 2026-08-30 01:22 UTCEPSS rescoreEPSS 0.6% · 43rd percentile
  62. 2026-08-28 20:25 UTCEG score recompute
  63. 2026-08-28 18:10 UTCEG score recomputeFirst assessed: 9.8 CRITICAL

Related CVEs(same product + same CWE)

Frequently asked(5)

What is CVE-2026-55559?
CVE-2026-55559 is a critical-severity vulnerability; its CVE record was 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 the CVE record for CVE-2026-55559 published?
The CVE record for CVE-2026-55559 was published on August 28, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of September 8, 2026; the record at its source may have been updated since.
Is CVE-2026-55559 actively exploited?
CVE-2026-55559 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.8% probability of exploitation in the next 30 days (54th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-55559?
CVE-2026-55559 has a CVSS base score of 9.8 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-55559?
A fix for CVE-2026-55559 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-55559 are linked in the Vendor Advisories panel on this page.

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