Learning from the Past: Notable Cases of Subdomain Takeover


In the realm of cybersecurity, learning from past incidents is crucial for preventing future threats. One such threat that has impacted several organizations is subdomain takeover. As we’ve discussed in previous articles, subdomain takeover occurs due to misconfigurations in DNS records, leading to potential data breaches and reputational damage. This article explores notable cases of subdomain takeover and the lessons we can learn from them.

Notable Cases of Subdomain Takeover

Over the years, several high-profile companies have fallen victim to subdomain takeover. Here are a few notable cases:

  1. Uber: In 2016, Uber experienced a subdomain takeover that exposed sensitive information about their drivers and passengers. The root cause was an unclaimed Amazon Web Services (AWS) S3 bucket linked to one of Uber’s subdomains. The attacker claimed the S3 bucket and was able to control the content served from the subdomain. This breach resulted in a settlement of $148 million for Uber, marking one of the most expensive subdomain takeover incidents to date.
  2. Slack: In 2017, a security researcher discovered a subdomain takeover vulnerability in Slack. The vulnerability was found in an unused Slack subdomain, *.status.slack.com. If exploited, it could have allowed an attacker to phish for user credentials or spread malware. Fortunately, this vulnerability was discovered and reported by a white-hat hacker before any damage was done.
  3. United Airlines: United Airlines faced a similar issue in 2017 when an unclaimed subdomain led to a takeover. The attacker could have used this to deface the website, phish for customer information, or distribute malware. United Airlines quickly resolved the issue once it was brought to their attention.

Lessons Learned

These cases highlight the potential dangers of subdomain takeover. Here are some key lessons that we can learn:

  1. Regular Auditing: Regularly auditing DNS records can help identify orphaned or misconfigured records that could lead to a subdomain takeover. As we discussed in our article on DNS Records, this is a crucial step in preventing subdomain takeover.
  2. Prompt Response: When vulnerabilities are identified, it’s important to respond promptly. This includes removing or updating orphaned DNS records and improving security measures.
  3. Continuous Monitoring: Using tools like bspeka’s Subdomain Takeover Monitor can help continuously monitor your subdomains for potential vulnerabilities.


Learning from past incidents of subdomain takeover is crucial for improving our cybersecurity measures. By understanding the mistakes that led to these incidents and implementing robust security measures, we can protect our online presence from potential threats.