CertSpotter
A lightweight Certificate Transparency log monitor that alerts you when SSL/TLS certificates are issued for your domains.
What is CertSpotter?
Cert Spotter is an open-source Certificate Transparency log monitor that alerts organizations when SSL/TLS certificates are issued for their domains. It helps detect security threats like DNS hijacking, subdomain takeovers, and unauthorized certificate issuance by monitoring public CT logs. The tool is designed to be lightweight, robust, and easier to deploy than other open-source alternatives.
Security teams, system administrators, and DevOps engineers responsible for domain and certificate management who need to monitor for unauthorized certificate issuance.
Developers choose Cert Spotter for its robust certificate parsing that ensures no missed certificates, its simplicity (no database required), and its security-focused design with defenses against attacks like null-byte prefix exploits.
Overview
Lightweight Certificate Transparency Log Monitor
Use Cases
Best For
- Detecting DNS hijacking attacks where attackers obtain certificates for compromised domains
- Monitoring for unauthorized certificate issuance outside corporate policy
- Identifying subdomain takeovers where abandoned subdomains are used maliciously
- Security teams needing lightweight CT log monitoring without database dependencies
- Organizations wanting self-hosted certificate transparency monitoring
- Preventing false alarms through authorized certificate whitelisting
Not Ideal For
- Teams requiring immediate, sub-minute alerts for certificate issuance
- Organizations without dedicated IT staff to manage command-line tools and daemons
- Projects needing out-of-the-box integration with modern chat platforms like Slack or Teams
- Users seeking a fully managed service with a graphical dashboard and zero configuration
Pros & Cons
Pros
Operates without a database, simplifying deployment and reducing maintenance overhead, as stated in the key features and README philosophy.
Uses a special parser that keeps certificates unparsed except for identifiers, ensuring no certificates are missed even with encoding errors, as detailed in the Security section to defend against adversarial attacks.
Implements defenses against null-byte attacks and correctly handles wildcard DNS names, enhancing detection accuracy for threats like subdomain takeovers, as explained in the Security section.
Supports email alerts and executable hooks for custom notification workflows, allowing integration with various systems, mentioned in the Quickstart and features.
Cons
Lacks direct support for popular notification platforms like Slack; users must rely on email or custom scripts, unlike the hosted service which offers these features, as indicated in the README comparison.
Requires creating configuration files, setting up daemons, and managing dependencies like sendmail, which can be cumbersome for non-technical users, as seen in the multi-step Quickstart instructions.
Features such as gossiping with other log monitors are planned for future releases but not currently available, limiting some audit capabilities, as noted in the Security section.
Frequently Asked Questions
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