Stop Staring at DNS Records
If you are new to Information Security, you’ll quickly learn that visibility is your best friend. One of the first things I look at when assessing a domain’s posture is its DMARC (Domain-based Message Authentication, Reporting, and Conformance) record. DMARC tells the world how to handle emails that claim to be from your domain but fail authentication. If a record is missing or set to p=none, an attacker can easily spoof your executive’s email address to launch a phishing campaign.
I wrote dmarc_check.sh to simplify this discovery phase. Instead of manually running dig commands for every sub-domain, this script automates the heavy lifting.
What this tool does for you:
- Rapid Assessment: It queries DNS for the _dmarc record and immediately classifies the risk level.
- Policy Logic: It distinguishes between “Secure” (reject), “Soft-Fail” (quarantine), and “Vulnerable” (none or missing).
- Bulk Reporting: For junior analysts managing large environments, the script processes entire lists of domains and outputs a clean CSV report for leadership.
Security doesn’t always require expensive enterprise suites. Often, it just requires a reliable script that turns raw data into actionable intelligence. Whether you are performing a bug bounty or hardening your first corporate network, this tool ensures you never miss a “low-hanging fruit” vulnerability.
Further Learning & Citations
To dive deeper into how DMARC works and why these specific flags matter, check out these essential resources:
- DMARC.org: Overview of DMARC Operations – The official definitive guide for the protocol.
- Cloudflare Learning: What is a DMARC DNS Record? – A great breakdown of the individual tags (p, rua, ruf).
- CISA (Cybersecurity & Infrastructure Security Agency): MS-ISAC Guide to DMARC – Government-level best practices for implementing email authentication.
- RFC 7489: Domain-based Message Authentication, Reporting, and Conformance (DMARC) – For those who want to read the actual technical specifications.