Compliance Impact

This vulnerability allows data exfiltration through a DNS covert channel by bypassing the configured HTTP/S-only egress allowlist in Docker Sandboxes. Such unauthorized data leakage could potentially lead to non-compliance with data protection regulations like GDPR and HIPAA, which require strict controls over sensitive data transmission and network security.

Because the vulnerability enables untrusted workloads to circumvent network policies and exfiltrate data without detection, organizations using Docker Sandboxes may face increased risk of data breaches or unauthorized data disclosures, impacting their compliance posture.

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Executive Summary

This vulnerability exists in Docker Sandboxes (sbx), where an HTTP/S-only egress allowlist is enforced but does not apply to DNS resolution.

The embedded DNS server forwards any DNS query to the host resolver if the network is internet-connected, without checking the allowlist policy.

As a result, an untrusted workload inside a sandbox can encode data into DNS labels for an attacker-controlled domain and exfiltrate data through a DNS covert channel, bypassing the configured allowlist.

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Detection Guidance

This vulnerability involves DNS resolution bypassing the HTTP/S-only egress allowlist by encoding data into DNS labels for attacker-controlled domains, enabling data exfiltration via DNS covert channels.

Detection on your network or system would involve monitoring DNS queries originating from Docker Sandboxes for unusual or suspicious domain names that could be used for data exfiltration.

Since the vulnerability relates to DNS queries bypassing policy, commands to monitor DNS traffic or logs on the host or sandbox network interfaces could help detect exploitation attempts.

• Use network packet capture tools like tcpdump or Wireshark to filter DNS traffic, e.g., `tcpdump -i <interface> port 53`.
• Inspect DNS query logs if available on your DNS server or embedded DNS resolver.
• Check sandbox network policies and logs for DNS requests to unusual or external domains.

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Mitigation Strategies

Immediate mitigation steps include restricting or monitoring DNS resolution from Docker Sandboxes to prevent unauthorized data exfiltration.

Since the vulnerability arises because the embedded DNS server forwards queries to the host resolver without policy enforcement, applying stricter network isolation and DNS resolution restrictions is recommended.

• Update Docker Sandboxes to the latest version that includes enhanced network isolation and DNS resolution restrictions as noted in recent releases.
• Configure sandbox network policies to explicitly control or block DNS queries to external domains.
• Monitor and audit DNS traffic from sandboxes for suspicious activity.
• Consider disabling or limiting sandbox internet connectivity if not required.

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Impact Analysis

This vulnerability allows an attacker to bypass network egress restrictions by using DNS queries to exfiltrate data covertly.

An untrusted workload running inside a Docker sandbox could leak sensitive information or data to an attacker-controlled domain via DNS, even if HTTP/S traffic is restricted.

This could lead to data breaches, unauthorized data disclosure, and compromise of confidentiality within environments using Docker Sandboxes.

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