Zscaler and DNS over HTTPS (DoH): Understanding Blocking and Bypass Techniques

DNS over HTTPS (DoH) is a protocol that encrypts DNS queries, enhancing user privacy and security. However, its encryption can present challenges for network security solutions like Zscaler, which often rely on inspecting DNS traffic for threat detection and policy enforcement. This article explores how Zscaler handles DoH traffic, why it might block it, and potential methods users might attempt to bypass these restrictions (though attempting to bypass security measures is generally discouraged unless explicitly authorized).

Why Zscaler Might Block or Inspect DoH

Zscaler's primary goal is to secure network traffic. Blocking or inspecting DoH traffic stems from several key concerns:

• Loss of Visibility: Encrypted DoH traffic prevents Zscaler from inspecting the DNS queries themselves. This limits its ability to identify malicious domains, phishing attempts, and command-and-control servers used in malware infections.
• Policy Enforcement: Zscaler enforces network policies, such as blocking access to specific websites or categories. Without visibility into DNS queries, enforcing these policies becomes significantly more difficult.
• Data Loss Prevention (DLP): Zscaler DLP features rely on analyzing DNS traffic to prevent sensitive data from leaving the network. DoH encryption can hinder this process.
• Threat Prevention: Zscaler's threat intelligence relies on analyzing DNS queries to identify potential threats. DoH encryption can obscure this critical information.

How Zscaler Handles DoH

Zscaler's approach to DoH varies depending on the configuration and the specific Zscaler deployment. Many organizations configure Zscaler to:

• Inspect DoH traffic (if possible): Zscaler may attempt to inspect DoH traffic through various techniques, leveraging features like deep packet inspection (DPI) or by partnering with DoH providers to obtain visibility into encrypted traffic. However, this is often limited and not always fully effective.
• Block DoH entirely: In some scenarios, organizations choose to completely block DoH traffic to maintain full visibility and control over their network.
• Allow DoH with specific resolvers: Some organizations might allow DoH, but only when using specific, trusted DNS resolvers that Zscaler can integrate with, providing a level of controlled visibility.

Potential (Discouraged) Bypass Techniques

Attempting to circumvent Zscaler's security measures is generally not recommended and can violate organizational policies. However, for informational purposes only, certain methods *might* be attempted, though their effectiveness varies and they're often quickly patched:

• Using a different DoH provider: Switching to a less commonly known or less heavily monitored DoH provider *might* temporarily evade detection, but this is often ineffective and unreliable.
• Using a VPN: A VPN can encrypt traffic before it reaches Zscaler, making it difficult to inspect. However, this is often blocked by Zscaler policies. Moreover, using an untrusted VPN might introduce further security risks.
• Configuring a local DNS server: Setting up a local DNS server and configuring devices to use it could bypass Zscaler's DNS inspection, but this requires technical expertise and careful configuration to avoid introducing new vulnerabilities.
• Using a proxy server: Similar to VPNs, using a proxy server can also mask your DNS traffic, though the same caveats apply regarding detectability and security concerns.

Table Summarizing Methods and Effectiveness

Disclaimer: This information is provided for educational purposes only. Attempting to bypass security measures is generally discouraged and may violate your organization's policies. Always prioritize secure and authorized methods for accessing online resources.