vulnerability / NVI-00010677 / Revision 2
kobako Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)
GitHub lists this reviewed advisory for kobako. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
10 critical
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
0.799%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.56562. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
kobako
source listed>= 0.1.0, <= 0.9.0
### 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: ```ruby 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
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-7pwq-q9jf-539h ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-55107 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.