Anthropic Sandbox Runtime is designed to provide lightweight OS-level sandboxing for processes by enforcing filesystem and network restrictions without the overhead of containerization. Prior to version 0.0.16, a vulnerability (CVE-2025-66479) existed due to a bug in the sandboxing logic related to network policy enforcement. Specifically, if the sandbox policy did not specify any allowed domains, the runtime failed to properly enforce network restrictions, effectively allowing sandboxed processes to make network requests outside the intended sandbox boundaries. This represents a protection mechanism failure (CWE-693) where the security control intended to restrict network access was bypassed. Exploitation requires the attacker to have high privileges on the host system (local vector with privileged access) but does not require user interaction. The vulnerability impacts the confidentiality and integrity of the sandbox environment by allowing unintended network communications, potentially leading to data exfiltration or command and control communications from sandboxed code. The vendor released a patch in version 0.0.16 that corrects the enforcement logic to ensure network restrictions are applied even when no allowed domains are configured. No public exploits or active exploitation have been reported to date. The CVSS 4.0 score is 1.8, reflecting low severity due to the requirement for privileged local access and limited impact scope.

For European organizations, the impact of this vulnerability is relatively low but not negligible. Organizations using anthropic-experimental sandbox-runtime in development, testing, or production environments could face risks if they rely on the sandbox for isolating untrusted or semi-trusted code. The failure to enforce network restrictions could allow malicious or compromised sandboxed processes to communicate externally, potentially leaking sensitive information or facilitating further attacks. However, the requirement for high privilege local access limits the likelihood of remote exploitation, reducing the overall risk. The vulnerability could be more impactful in environments where sandbox-runtime is used to isolate critical workloads or where network isolation is a key security control. European organizations in sectors with high security requirements, such as finance, critical infrastructure, or research institutions, should be particularly attentive. Since no known exploits exist in the wild, the immediate threat is low, but the vulnerability should be addressed proactively to maintain strong security postures.

1. Upgrade anthropic-experimental sandbox-runtime to version 0.0.16 or later immediately to apply the patch that fixes the network enforcement bug. 2. Review sandbox policies to ensure that network restrictions are explicitly defined and tested to prevent accidental misconfigurations. 3. Limit privileged local access to systems running sandbox-runtime to trusted administrators only, reducing the risk of exploitation. 4. Implement monitoring and alerting for unusual network activity originating from sandboxed processes to detect potential misuse. 5. Conduct regular security audits and penetration tests focusing on sandbox environments to validate the effectiveness of isolation controls. 6. Consider additional layers of network segmentation and host-based firewall rules to complement sandbox network restrictions. 7. Educate developers and system administrators about the importance of applying security patches promptly and verifying sandbox configurations.