Watering Hole Attacks - Compromising Trusted Sites

About 2 min read

A watering hole attack is a type of targeted attack in which attackers identify and compromise in advance the websites that employees of a target organization or industry frequently visit, then infect visitors' devices with malware. The name comes from an analogy to a predator lying in wait at a watering hole where wild animals gather. In 2024 as well, watering hole attacks by state-sponsored threat groups were confirmed on multiple industry association websites, making it a technique that remains very active.

The Premise That Familiar Places Cannot Be Verified

What makes this technique work is that the side doing the visiting has no means of verifying the state of the place being visited. The places used in daily work are not under the visitors control, and there is no way to tell from outside what has been swapped in there. What is more, the more frequently a place is used, the more the very act of opening it as usual creates a situation in which no reason to doubt ever arises. Familiarity, then, is not a lapse of attention; it is the result of there being structurally no occasion to verify. Next, where a mechanism is in place that varies what is returned according to the origin of the incoming request, what the verifying party sees and what was actually delivered become two different things. Under that structure, the result of opening the same place later and finding nothing happening is no confirmation that nothing was delivered. The fact that it does not reproduce is itself treated as an indication that conditions may have been attached to what is returned. The question that therefore remains is when the material for connecting things is prepared. Traces left on the other side cannot be inspected, and what remains on ones own side is only two records: where the traffic went, and what happened afterwards. These two connect only when set against each other, and setting them against each other requires both to have been retained from ordinary times. They cannot be started after something unusual has been noticed.

Watering Hole Attack Flow

How the Attack Unfolds

First, attackers research the industry news sites, technical forums, and industry association sites that the target organization's employees frequently visit. Next, they exploit the vulnerabilities of those sites to embed malicious scripts. By carrying out a "selective attack" that delivers malware only to access from the target organization's IP address range, they evade detection by security researchers. Unlike spear phishing, the troublesome point is that it cannot be blocked by email filters.

Defensive Measures

Defending against watering hole attacks requires a multi-layered approach. Keep browsers and plugins up to date to close vulnerabilities other than zero-days, and use web proxies and sandboxes to detect the execution of suspicious scripts. At the network level, detecting anomalous communication patterns with IDS/IPS is effective. Monitor malware behavior with endpoint EDR (Endpoint Detection and Response) and aim for early detection of infections. It is also important to protect each account with a unique, strong password for every service, preventing the damage from spreading after a malware infection.