The publishing world faces a critical security threat that remains largely overlooked. A dangerous Substack vulnerability allows attackers to hijack abandoned subdomains, potentially damaging your brand and misleading your audience. This security flaw stems from how Substack handles DNS configurations and domain verification—or rather, the lack thereof.
When you create a Substack newsletter with a custom subdomain like “newsletter.yourdomain.com,” you set up a CNAME record pointing to Substack’s servers. The vulnerability emerges when publishers abandon these newsletters without removing the DNS records. Unlike many platforms that verify domain ownership, Substack permits anyone to claim an abandoned subdomain by simply paying a fee—no ownership verification required.
This creates a perfect storm for malicious actors. If you’ve left old CNAME records pointing to Substack, someone could claim your subdomain, publish content under your domain name, and potentially harm your reputation or readers.
The risk is particularly severe for organizations managing multiple digital properties. Marketing teams might launch experimental newsletters, later abandoning them without properly closing accounts or removing DNS records. Each forgotten configuration becomes a potential entry point for attackers.
What makes this Substack DNS exploitation particularly dangerous is its legitimacy. Since the attacker publishes through official Substack channels on a subdomain that genuinely belongs to your domain, the content appears completely authentic to readers. Standard security tools won’t flag these takeovers because the DNS configuration remains technically correct.
To protect yourself from this vulnerability, take these immediate steps:
- Audit all your DNS records, specifically identifying CNAME records pointing to Substack’s infrastructure
- Properly deactivate any unused Substack publications through their platform
- Remove abandoned CNAME records from your DNS configuration
- Document all active subdomains in a centralized inventory
For ongoing protection, implement quarterly DNS reviews focusing on third-party publishing connections. Monitor for unexpected subdomain activity and consider certificate transparency monitoring to alert you when new SSL certificates are issued for your domains.
Consider a common scenario: A company experiments with a Substack newsletter at “insights.companyname.com” for several months before moving their content strategy elsewhere. They disable the newsletter but forget about the DNS record. Later, an attacker discovers this abandoned subdomain and claims it through Substack. Within hours, they’ve created a convincing replica of the company’s branding and begun publishing malicious content that appears to come from a legitimate company source.
The reputational damage can be substantial—readers trust content coming from your actual domain, making them more likely to share sensitive information or follow harmful advice when it appears to come from a trusted source.
The most effective protection remains vigilance. Treat your DNS records as critical infrastructure requiring regular maintenance and monitoring. Prioritize platforms that verify domain ownership through DNS TXT records or file uploads when selecting publishing tools.
By understanding this Substack vulnerability and implementing proper DNS hygiene, you can significantly reduce your risk exposure while continuing to leverage the benefits of distributed publishing platforms.
