CVE-2026-55107

CRITICALPre-NVD 10.010.0
EchelonGraph scoreMEDIUM confidence

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

Score 10.0 from GitHub Security Advisory (severity: CRITICAL) published 2026-08-18. A secondary CVSS source baseline 10.0; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, a secondary CVSS source
Trending — 3 sources updated this weekElevated

Also known asEUVD-2026-90197 (ENISA EUVD) · GHSA-7pwq-q9jf-539h (GitHub Security Advisories)Source: ENISA EUVD

10.0EG
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: 10.0Exploit: No code on recordExposed services: Not assessed

A fix is available — apply it.

Kobako is a Ruby gem that embeds a Wasm-isolated mruby interpreter inside applications, allowing execution of untrusted Ruby scripts (LLM-generated code, user formulas, student submissions, third-party plugins) in-process without giving them access to host memory, files, network, or credentials. From version 0.1.0 to before version 0.9.1, a guest mruby script running inside the Kobako sandbox can execute arbitrary Ruby in the host process, fully escaping the sandbox. This issue has been patched in version 0.9.1.

CVSS v3
10.0
EG Score
10.0CRITICALmedium confidence
EG Risk
76
EG Risk 76/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity100% × 45%
Impact severity (EG Severity): CVSS 10.0 of 10. Never the KEV-floored or EPSS-lifted EG Score.
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
56th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (10.0): severity, escalated by confirmed exploitation. This CVE's 10.0 is its impact severity (EG Severity), not escalated.

EG Severity
10.0 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
0.8% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-01). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track* at medium mission impactTrack at low, Track* at medium and Attend at high mission impact.CISA BOD 26-04: 3 days if the affected system is publicly exposed; 60 days if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.

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.

The score's inputs: 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 18, 2026

Last Modified

September 30, 2026

Advisory Details (3)

Auto-updated Oct 30, 2026
🔬 Proof of concept available. Patch available. Sources: github_commit, github_release, github.
GitHub advisoryMentions a patch (unverified)🟡 PoC Available

Sandbox escape: guest eval reaches host RCE via method_missing → public_send (any bound Service) · Advisory · elct9620/kobako · GitHub

Affected: 0.9.1. The dispatcher now rejects any method whose resolved owner is

https://github.com/elct9620/kobako/security/advisories/GHSA-7pwq-q9jf-539h
GitHub release Patch Available

v0.9.1

Patch available: elct9620/kobako v0.9.1

https://github.com/elct9620/kobako/releases/tag/v0.9.1
GitHub commit

commit 64f84700c81f (elct9620/kobako)

Fix landed in elct9620/kobako commit 64f84700c81f — awaiting tagged release

https://github.com/elct9620/kobako/commit/64f84700c81f44902bed9211318d5362f44987b3

Vendor Advisories for CVE-2026-55107(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(1)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
rubygemskobako @ 0.9.1 (fixes >= 0.1.0, <= 0.9.0)—ghsa

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(1 across 1 ecosystem)
RubyGems(1)
PackageVulnerable rangeFix by version rangeDependents
kobako0.1.0 ... 0.9.0 (14 versions)
  • 0.1.0 up to 0.9.1: fixed in 0.9.1
—

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 16× in last 7d / 62× 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. 2026-11-01 23:30 UTCEG score recompute
  2. 2026-11-01 23:30 UTCGHSA enrichmentGHSA-7pwq-q9jf-539h · GitHub severity CRITICAL · GitHub CVSS 10.0
  3. 2026-11-01 07:44 UTCGHSA enrichmentGHSA-7pwq-q9jf-539h · GitHub severity CRITICAL · GitHub CVSS 10.0
  4. 2026-11-01 07:44 UTCEG score recompute
  5. 2026-11-01 00:43 UTCEG score recompute
  6. 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.8% · 56th percentile
  7. 2026-10-31 01:55 UTCEG score recompute
  8. 2026-10-30 16:34 UTCEPSS rescoreEPSS 0.8% · 56th percentile
  9. 2026-10-30 03:08 UTCEG score recompute
  10. 2026-10-29 16:33 UTCEPSS rescoreEPSS 0.8% · 56th percentile
  11. 2026-10-29 04:21 UTCEG score recompute
  12. 2026-10-28 16:32 UTCEPSS rescoreEPSS 0.8% · 56th percentile
  13. 2026-10-28 05:26 UTCEG score recompute
  14. 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.8% · 56th percentile
  15. 2026-10-27 06:38 UTCEG score recompute
  16. 2026-10-26 16:31 UTCEPSS rescoreEPSS 0.8% · 56th percentile
  17. 2026-10-26 04:12 UTCEG score recompute
  18. 2026-10-25 16:33 UTCEPSS rescoreEPSS 0.8% · 56th percentile
  19. 2026-10-25 14:19 UTCEG score recompute
  20. 2026-10-25 05:25 UTCEG score recompute
  21. 2026-10-24 16:33 UTCEPSS rescoreEPSS 0.8% · 56th percentile
  22. 2026-10-24 06:37 UTCEG score recompute
  23. 2026-10-23 16:32 UTCEPSS rescoreEPSS 0.8% · 56th percentile
  24. 2026-10-23 07:47 UTCEG score recompute
  25. 2026-10-22 16:34 UTCEPSS rescoreEPSS 0.8% · 56th percentile
Show 47 more
  1. 2026-10-22 08:55 UTCEG score recompute
  2. 2026-10-21 16:33 UTCEPSS rescoreEPSS 0.8% · 56th percentile
  3. 2026-10-21 10:06 UTCEG score recompute
  4. 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  5. 2026-10-20 11:14 UTCEG score recompute
  6. 2026-10-19 16:32 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  7. 2026-10-19 12:26 UTCEG score recompute
  8. 2026-10-18 16:32 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  9. 2026-10-18 03:30 UTCEG score recompute
  10. 2026-10-17 16:34 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  11. 2026-10-17 11:56 UTCEG score recompute
  12. 2026-10-16 16:42 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  13. 2026-10-16 13:06 UTCEG score recompute
  14. 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  15. 2026-10-15 14:17 UTCEG score recompute
  16. 2026-10-14 16:33 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  17. 2026-10-14 09:02 UTCEG score recompute
  18. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  19. 2026-10-13 05:43 UTCEG score recompute
  20. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  21. 2026-10-12 15:56 UTCEG score recompute
  22. 2026-10-11 19:39 UTCEG score recompute
  23. 2026-10-11 16:54 UTCEG score recompute
  24. 2026-10-11 14:17 UTCEG score recompute
  25. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  26. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  27. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  28. 2026-10-08 17:12 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  29. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  30. 2026-10-06 17:06 UTCEG score recompute
  31. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  32. 2026-10-06 08:21 UTCEG score recompute
  33. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  34. 2026-10-05 01:53 UTCEG score recompute
  35. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  36. 2026-10-03 17:37 UTCEG score recompute
  37. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  38. 2026-10-02 18:59 UTCEG score recompute
  39. 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  40. 2026-10-02 01:25 UTCEG score recompute
  41. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.9% · 58th percentile
  42. 2026-10-01 01:28 UTCEG score recompute
  43. 2026-09-30 20:04 UTCEG score recompute
  44. 2026-09-30 19:56 UTCEG score recompute
  45. 2026-09-30 18:42 UTCEG score recompute
  46. 2026-09-28 21:55 UTCEG score recompute
  47. 2026-08-18 20:41 UTCEG score recomputeFirst assessed: 10.0 CRITICAL

Frequently asked(5)

What is CVE-2026-55107?
CVE-2026-55107 is a critical-severity vulnerability; its CVE record was published on August 18, 2026. Kobako is a Ruby gem that embeds a Wasm-isolated mruby interpreter inside applications, allowing execution of untrusted Ruby scripts (LLM-generated code, user formulas, student submissions, third-party plugins) in-process without giving them access to host memory, files, network, or credentials.…
When was the CVE record for CVE-2026-55107 published?
The CVE record for CVE-2026-55107 was published on August 18, 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 30, 2026; the record at its source may have been updated since.
Is CVE-2026-55107 actively exploited?
CVE-2026-55107 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.8% probability of exploitation in the next 30 days (56th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-55107?
CVE-2026-55107 has a CVSS base score of 10.0 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-55107?
A fix for CVE-2026-55107 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-55107 are linked in the Vendor Advisories panel on this page.

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