Code Injection in kobako (CVE-2026-55107)
Summary
Code injection in kobako (CVE-2026-55107). Successful exploitation can lead to full system takeover. Exploitable via public_send. Mitigation: upgrade to 0.9.1 or later.
Original description
The description as published by the source.
Summary
A guest mruby script running inside the Kobako sandbox can execute arbitrary
Ruby in the host process, fully escaping the sandbox.
Details
A host embeds bound "Service" objects that guest scripts call across the wasm
boundary through the transport dispatcher. The dispatcher passed the
guest-supplied method name straight to Object#public_send on the bound
object, with no restriction to the object's own methods:
target.public_send(method.to_sym, *args, **kwargs, &block)
public_send can invoke any public method, including Ruby's ambient
reflection surface. A guest pivots through the public send into otherwise
private Kernel methods: a dispatch request with method = "send" and
args = [:eval, ""] evaluates to target.send(:eval, ""),
running attacker-controlled Ruby in the host. Any bound Service object is
sufficient — no Service-specific behavior is required.
Proof of Concept
A guest call equivalent to:
Service.send(:eval, "")
executes in the host process and can read or modify host state, spawn
processes, and so on.
Impact
Complete sandbox escape leading to remote code execution in the host process,
defeating the gem's central guarantee of isolating untrusted mruby scripts.
Any deployment that runs untrusted or attacker-influenced scripts is affected.
All released versions (0.1.0 through 0.9.0) are vulnerable; the dispatcher
carried the same unguarded public_send sink under three successive names
(registry → rpc…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-55107 has been found in kobako.
Attackers can target a specific entry point like public_send over the network to misuse the product.
Successful exploitation can lead to full system takeover. CVSS score: 10.0/10.
What to do: upgrade kobako to 0.9.1 or later.
If unsure, ask your IT team or search "kobako CVE-2026-55107" on the vendor's site.
CVE-2026-55107 (kobako) — CWE-94 / CVSS v3 10.0
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: public_send / send / registry / rpc
Patched: 0.9.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Arbitrary code execution (CWE-94) exists in kobako. Attackers reach the vulnerable code path via public_send without authentication.
Check the vendor advisory for the affected versions of kobako. Attack surface: public_send / send / registry / rpc.
Severity: Critical (CVSS 10.0/10). Successful exploitation can lead to full system takeover.
Update to 0.9.1.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'kobako' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'kobako' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
kobakoを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade kobako to 0.9.1ステージング環境で 0.9.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- package github.com
- web github.com
- web github.com
- web github.com
- web security-advisories@github.com