Bottom line: An insecure customer endpoint allowed outsiders to access sandbox resources, not a flaw in Modal’s platform itself.
A Modal customer had made an unauthenticated API endpoint publicly accessible, through which any user on the internet could execute code in that customer’s sandboxes. A rogue automated agent whose behavior recently garnered attention also exploited this vulnerability.
Modal CTO Akshat Bubna confirmed to Reuters that a customer of the Modal cloud-compute platform had publicly exposed an unauthenticated endpoint. This enabled anyone on the internet to use that customer’s sandboxes to execute arbitrary code.
The rogue agent used this method to gain access to the environment. For CISOs, this represents a classic case of misconfigured infrastructure in customer ownership: a missing authentication layer combined with overly broad network access permissions.
Bubna explicitly emphasized that neither Modal’s platform architecture nor its isolation mechanisms were compromised. The security failure lay in the configuration and lack of API key management on the customer side. For operators of cloud sandboxes, a reminder to review endpoint authentication and network policies.
Source: simonwillison.net · Published 29 July 2026
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