A user is puzzled by how their subdomain, used for internal documentation and not linked anywhere publicly, was discovered and accessed by an external user. They're concerned about potential security vulnerabilities and are seeking explanations for how this could have happened, considering they haven't shared the subdomain's address. The user is ruling out DNS brute-forcing due to the subdomain's unique and unguessable name. They're particularly perplexed because the subdomain isn't indexed by search engines and hasn't been exposed through any known channels.
The author of the Hacker News post expresses bewilderment over how their subdomain, specifically something.theirdomain.com, was discovered and subsequently accessed by external users. They articulate that this subdomain hosts an internal application, intentionally not linked from anywhere publicly accessible on their main domain, theirdomain.com. Furthermore, they emphasize that the subdomain is not indexed by any search engines, nor have they shared its address in any public forum or communication. This leads them to question the possible mechanisms by which external parties could have learned of its existence and successfully navigated to it. The author is particularly curious to understand if there are common vulnerabilities or overlooked aspects of web server configurations that might inadvertently expose subdomains meant to remain private. They are seeking insights from the Hacker News community regarding potential explanations for this unexpected discovery, hoping to understand how it occurred and implement measures to prevent similar occurrences in the future. The author implicitly indicates a desire to maintain the privacy of this internal application while acknowledging its current, unintended visibility.
Summary of Comments ( 188 )
https://news.ycombinator.com/item?id=43285725
The Hacker News comments discuss various ways a subdomain might be discovered, focusing on the likelihood of accidental discovery rather than malicious intent. Several commenters suggest DNS brute-forcing, where automated tools guess subdomains, is a common occurrence. Others highlight the possibility of the subdomain being included in publicly accessible configurations or code repositories like GitHub, or being discovered through certificate transparency logs. Some commenters suggest checking the server logs for clues, and emphasize that finding a subdomain doesn't necessarily imply anything nefarious is happening. The general consensus leans toward the discovery being unintentional and automated.
The Hacker News post "Ask HN: How did the internet discover my subdomain?" generated several comments offering various explanations and suggestions to the original poster (OP).
Several commenters focused on the likelihood of DNS propagation. They explained that even though the OP believed they hadn't publicly exposed their subdomain, the very act of configuring it within their DNS settings likely triggered its propagation across DNS servers. This means the subdomain became visible to parts of the internet, potentially through DNS queries made by various entities, including search engine crawlers, security scanners, or even malicious bots actively scanning for new domains.
Another popular theory revolved around misconfigured services or exposed APIs. Commenters suggested the possibility of a service running on the subdomain being inadvertently accessible from the public internet, perhaps due to a firewall misconfiguration or overly permissive access rules. They also suggested checking for publicly accessible APIs that might have revealed the subdomain's existence.
Some comments touched upon the possibility of certificate transparency logs. These logs publicly record SSL/TLS certificates issued for websites, and if the OP had obtained a certificate for their subdomain, it would be logged and thus discoverable.
A few commenters mentioned the potential role of link rot analysis tools and web crawlers. These tools constantly scan the web for broken links, and if a link to the OP's subdomain existed somewhere, even if obscure or unintended, it could have been discovered this way. Likewise, generic web crawlers might have stumbled upon the subdomain through various means and indexed it.
Several users offered practical advice to the OP, recommending using tools like
digto trace DNS records and identify potential points of exposure. Others advised checking server logs for any unusual activity that might indicate how the subdomain was discovered.A more speculative, but still plausible suggestion, involved the possibility of the subdomain being guessed or brute-forced. While less likely for a complex or randomly generated subdomain name, it is not impossible, particularly if the name is based on common patterns or easily guessable words.
Finally, some comments highlighted the inherent difficulty of fully controlling information propagation on the internet. Once something is even briefly exposed, it can be difficult to completely erase its trace. They emphasized the importance of proactive security measures and careful configuration to minimize unintended exposure.