kobako Sandbox Escape Vulnerability: Early Warning and Mitigation
- Severity
- HIGH
- Affected component
- kobako (gem)
- Affected versions
- >= 0.1.0, < 0.9.1 or >= 0.1.0, <= 0.1.0 or >= 0.1.1, <= 0.1.1 or >= 0.1.2, <= 0.1.2 or >= 0.2.0, <= 0.2.0 or >= 0.2.1, <= 0.2.1 or >= 0.3.0, <= 0.3.0 or >= 0.4.0, <= 0.4.0 or >= 0.5.0, <= 0.5.0 or >= 0.6.0, <= 0.6.0 or >= 0.6.1, <= 0.6.1 or >= 0.6.2, <= 0.6.2 or >= 0.7.0, <= 0.7.0 or >= 0.8.0, <= 0.8.0 or >= 0.9.0, <= 0.9.0
- Patched version
- 0.9.1
An early warning has been issued regarding a sandbox escape vulnerability in the kobako gem. This vulnerability allows a guest mruby script to execute arbitrary Ruby code in the host process, fully escaping the sandbox.
What happened
An early warning has been issued for a high-severity supply-chain vulnerability in the kobako gem. The vulnerability, tracked as GHSA-7PWQ-Q9JF-539H, allows a guest mruby script running inside the Kobako sandbox to execute arbitrary Ruby code in the host process, fully escaping the sandbox. This is achieved through the method_missing → public_send mechanism, which can be exploited by any bound Service. The vulnerability affects all versions of kobako gem from 0.1.0 to 0.9.0.
The issue was first flagged on 2026-08-18T20:09:59+00:00. It is currently under investigation and has not been reported as exploited in the wild. The recommended action to mitigate this vulnerability is to upgrade to kobako@0.9.1.
What to do about it
- Identify all instances of kobako gem in your software supply chain.
- Check the version of kobako gem being used. If it is between 0.1.0 and 0.9.0, it is affected.
- Upgrade to kobako@0.9.1 to mitigate the sandbox escape vulnerability.
- Monitor the primary sources for any updates or additional information regarding this vulnerability.
How 0Day would have caught this
kobako is anywhere in your dependency tree, the engineers who own the affected repositories get a push alert the moment it is flagged — no manual audit to remember to run.Read how this differs from waiting on a scanner to catch a known advisory, or see the exact, read-only access 0Day needs to do this for an organization.
Frequently asked questions
Am I affected?
If you are using kobako gem in versions between 0.1.0 and 0.9.0, you are affected.
What should I do right now?
Upgrade to kobako@0.9.1 to mitigate the sandbox escape vulnerability.
Has this been exploited in the wild?
There are no reports of this vulnerability being exploited in the wild at this time.