CVE-2026-55107

CRITICALPre-NVD 10.010.0—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 10.0 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.8% (55th percentile of EPSS-scored CVEs). 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
Elevated
10.0EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.8%CVSS: 10.0Exploit: Elevated riskExposed 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 76/100CISA SSVC

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
Severity100% × 45%
Exploitation40% × 40%
Automatability100% × 15%
CISA SSVC: Track at low, Track* at medium and Attend at high mission impact.
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
55th
KEV
Not listed

CISA SSVCTrack 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). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

August 18, 2026

Last Modified

September 30, 2026

Advisory Details (3)

Auto-updated Sep 30, 2026
🔬 Proof of concept available. Patch available. Sources: github_commit, github_release, github.
github Patch Available🟡 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 Patch Available

commit 64f84700c81f (elct9620/kobako)

Patch available: elct9620/kobako kobako-mruby-v0.15.0 (contains commit 64f84700c81f)

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.

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 13× in last 7d / 13× 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.

  1. 2026-10-05 01:53 UTCEG score recompute
  2. 2026-10-04 23:22 UTCEPSS rescore
  3. 2026-10-03 17:37 UTCEG score recompute
  4. 2026-10-03 14:26 UTCEPSS rescore
  5. 2026-10-02 18:59 UTCEG score recompute
  6. 2026-10-02 17:56 UTCEPSS rescore
  7. 2026-10-02 01:25 UTCEG score recompute
  8. 2026-10-01 19:50 UTCEPSS rescore
  9. 2026-10-01 01:28 UTCEG score recompute
  10. 2026-09-30 20:04 UTCEG score recompute
  11. 2026-09-30 19:56 UTCEG score recompute
  12. 2026-09-30 18:42 UTCEG score recompute
  13. 2026-09-28 21:55 UTCEG score recompute
  14. 2026-08-18 20:41 UTCEG score recompute

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-55107?
CVE-2026-55107 is a critical vulnerability 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 CVE-2026-55107 disclosed?
CVE-2026-55107 was first published on August 18, 2026, with the most recent update on September 30, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
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 (55th 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.

Dependency Blast Radius

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