Full Report
Joff Thyer // The Domain Name System (DNS) is the single most important protocol on the Internet. The distributed architecture of DNS name servers and resolvers has resulted in a […] The post Tap Into Your Valuable DNS Data appeared first on Black Hills Information Security, Inc..
Analysis Summary
# Best Practices: Secure and Scalable DNS Logging via DNSTAP
## Overview
These practices focus on establishing robust and high-performance logging for Domain Name System (DNS) operations. Traditional synchronous logging methods on high-load DNS servers (like Microsoft DNS or BIND) degrade performance due to disk I/O bottlenecks. The recommended approach utilizes the DNSTAP protocol to decouple logging serialization from core DNS server operations, ensuring valuable security and operational intelligence is reliably captured without degrading service performance.
## Key Recommendations
### Immediate Actions
1. **Identify Performance Bottlenecks:** Audit existing DNS server configurations to ensure "debug logging" (on Microsoft DNS) or synchronous logging features (on BIND) are **disabled** to prevent performance degradation and log loss, especially under high load.
2. **Adopt DNSTAP Concept:** Prioritize implementing a solution that separates DNS I/O from log output, such as adopting the DNSTAP protocol for querying and response capture.
3. **Install Core Dependencies for DNSTAP Development/Testing:** On a development/build machine (not the production DNS server), install essential build tools and dependencies required for compiling BIND with DNSTAP support or installing necessary logging components:
* Install system build tools (`build-essential`, `libtool`, `autoconf`, `automake`, `libssl-dev` on Ubuntu systems).
* Install Google protocol buffer dependencies (`libprotobuf-c-dev`, `libprotobuf-c1`, `protobuf-c-compiler`).
* Install Frame Stream tools (`fstrm-bin`, `libfstrm0`, etc., or compile from source).
### Short-term Improvements (1-3 months)
1. **Source Compilation for DNSTAP Support:** If using ISC BIND and the distribution package lacks DNSTAP support (e.g., on older patching versions), manually compile the BIND server from source on a dedicated build environment, ensuring DNSTAP features are correctly integrated.
2. **Deploy DNSTAP Receiver:** Implement receiver software capable of ingesting the serialized binary stream generated by the DNSTAP-enabled DNS server.
3. **Configure Log Reading Utility:** Deploy and configure the `dnstap-read` utility (provided with the ISC BIND distribution) on a separate analysis station to test and validate the integrity and completeness of the captured binary logs.
### Long-term Strategy (3+ months)
1. **Integrate Log Analysis Pipeline:** Integrate the DNSTAP binary logs into a Security Information and Event Management (SIEM) system or dedicated log analysis platform capable of parsing binary protocol buffers.
2. **Develop Custom Parsers (If Necessary):** Implement custom analysis scripts (e.g., using Python frameworks that parse frame stream logs) to generate specific security metrics and visualizations beyond basic reading.
3. **Establish Baseline and Anomaly Detection:** Use the comprehensive, non-degrading logs captured via DNSTAP to establish a baseline of normal DNS lookups (AUTH\_QUERY, RESOLVER\_RESPONSE, etc.). Configure monitoring to alert on anomalies (e.g., suspicious external lookups, high volumes of traffic to sinkholes).
## Implementation Guidance
### For Small Organizations
- Focus on ensuring the DNS server (especially if hosting internal records) is configured to output DNSTAP logs, even if initial log analysis is manual or basic.
- If performance is not currently an issue, prioritize setting up the DNSTAP receiver component first, which offloads the I/O, while gradually migrating the DNS core service to a DNSTAP-enabled binary.
### For Medium Organizations
- Dedicate a separate, low-capacity system to act as the DNSTAP collector/receiver and initial log archive. This insulates the DNS server completely from log writing operations.
- Utilize readily available binaries or packages for `fstrm` and Protocol Buffers, minimizing custom compilation unless necessary for the exact upstream version used.
### For Large Enterprises
- Treat DNS logging as a critical data source equivalent to network flow data. Consider deploying specialized security sensors (like Bro/Zeek, if applicable) configured to listen to mirrored network traffic (SPAN/tap) upstream of the DNS servers as a redundant capture mechanism, although DNSTAP is the primary source for high-fidelity data.
- Implement load-balanced, high-availability DNSTAP receivers and ensure logging infrastructure scales appropriately, utilizing high-speed storage optimized for sequential write operations to handle the resulting binary stream.
## Configuration Examples
**Dependency Installation (Ubuntu Example):**
bash
# Install build dependencies
sudo apt update
sudo apt install build-essential libtool autoconf automake libssl-dev
# Install Protocol Buffer and Frame Stream dependencies
sudo apt install libprotobuf-c-dev libprotobuf-c1
sudo apt install protobuf-c-compiler
sudo apt install fstrm-bin libfstrm0 libfstrm-dev libfstrm0-dbg
**ISC BIND DNSTAP Configuration (Conceptual - Requires recompilation):**
*(Specific configuration syntax depends on the compilation process, but the goal is to enable the DNSTAP output feature within the BIND `options` block to direct output to a designated byte stream.)*
**Reading DNSTAP Logs using `dnstap-read`:**
bash
# Read all default output from a log file
dnstap-read /path/to/your/dnstap.log
# Read log data and print the full DNS message payload (like 'dig' output)
dnstap-read -p /path/to/your/dnstap.log
# Output data in YAML format for easier parsing
dnstap-read -y /path/to/your/dnstap.log
**Log Message Types Captured:**
The system captures detailed message types: AUTH\_QUERY (AQ), AUTH\_RESPONSE (AR), RESOLVER\_QUERY (RQ), RESOLVER\_RESPONSE (RR), CLIENT\_QUERY (CQ), CLIENT\_RESPONSE (CR), etc.
## Compliance Alignment
- **NIST SP 800-92 (Guide to Computer Security Log Management):** DNSTAP directly addresses the requirement for comprehensive logging of network services, providing immutable, detailed records necessary for auditing.
- **ISO/IEC 27002 (A.12.4.1 - Event Logging):** Ensures that logs capturing critical infrastructure services like DNS are captured reliably without impacting service availability.
- **CIS Benchmarks (Network Security Monitoring):** Provides the raw query/response data required for effective network traffic analysis and detection of command-and-control (C2) communications carried over DNS.
## Common Pitfalls to Avoid
1. **Leaving Debug Logging Enabled:** Do not use native "debug logging" features on DNS servers (e.g., Microsoft DNS debug logging) for continuous production monitoring, as this causes severe I/O contention and may result in lost log entries.
2. **Synchronous File I/O:** Avoid relying on conventional synchronous logging methods for high-volume DNS servers, as disk write operations will always introduce performance penalties and potential data loss when the server prioritizes request servicing.
3. **Assuming Default BIND Builds Support DNSTAP:** Many OS distributions do not include DNSTAP support compiled into their default BIND packages; manual compilation from source may be required to enable this feature.
## Resources
- **DNSTAP Protocol Information:** http://dnstap.info/
- **ISC BIND Source Compilation Tutorials:** Referencing community guides related to compiling BIND with specific security modules (search for "ISC BIND DNSTAP compilation").
- **Example Python Parser (for analysis):** https://github.com/yoda66/DNSTAP-FrameStream-Python
- **Farsight Security GitHub (Source for related tools):** https://github.com/farsightsec