Cybercrooks are now creating live, personalized phishing pages in real time

At first glance, it’s a normal and harmless webpage, but it’s able to transform into a phishing site after a user has already loaded it. In a matter of a few seconds, AI carefully crafts a landing page specifically for the victim, thus turning it into an online crime scene.

Researchers have demonstrated an unusual phenomenon in which seemingly innocent webpages can use AI to create and run malicious JavaScript in the victim's browser while the victim is visiting the page.

Although the type of attack is relatively new, the outcome is traditional – victims end up losing their personal information, often without ever knowing they’ve visited dangerous areas of the internet.

Here’s how it happens.

Firstly, the attackers select a webpage from an existing phishing campaign and use it as a model for the malicious behaviour they want their own campaign to replicate.

The malicious code is difficult to trace because it’s polymorphic – it’s generated on the spot by demand, therefore, it slightly differs with each visit. It’s an aspect that makes this scheme all the more clever – because the code’s “transformation” happens within the victim’s browser, the landing page will:

• It looks very convincing because it will be based on data the browser stores, such as the user’s language, location, or device type.
• Have a somewhat “reusable” malicious link, because every victim will see a version that’s crafted especially for them.

It gets worse.

These scammers carefully craft AI prompts that “persuade” AI systems to generate small snippets of malicious JavaScript code. They come from trusted AI providers, such as DeepSeek or Google Gemini, which in turn allows the code to slip through network security checks without raising any red flags.

“Subsequently, these generated scripts could be assembled and executed to render malicious code or phishing content,” explains the research by Unit42.

During the few moments it takes for this to happen, ”the snippets are assembled and executed in the browser's runtime environment,” thus making the webpage on which the user is visiting fully capable of stealing login details or other sensitive information.

Researchers recreated this scam themselves and found a catch

In order to check how this scam works in practice, a group of researchers partially recreated it themselves.

After following all the steps, researchers found that the words used to generate the malicious AI code matter a great deal. Researchers did not disclose which LLMs they were using, but stated that they refused to act upon obviously malicious instructions. However, a change in wording to make it sound more vague did the trick.

For example, “a request for a generic $AJAX POST function was permitted, while a direct request for 'code to exfiltrate credentials' was blocked. Furthermore, indicators of compromise could also be hidden within the prompt itself to keep the initial page clean,” the paper explains.

One of the risks of running this type of attack, according to researchers, is the possibility that the LLM model might hallucinate some of its elements. However, the attack they simulated was successful.

How to avoid this type of attack?

Although the attack is rather sneaky, there are several ways to combat the danger or avoid it altogether.

Firstly, these AI-powered phishing attacks could be prevented by “runtime behavioral analysis,” which, in practice, signals the need to monitor and block malicious behavior directly in browsers where the attacks occur.

Another idea is to perform “offline analysis with browser-based sandboxes that render the final webpage” before someone visits it.

Finally, researchers emphasize that their study highlights the need for more “robust safety guardrails in LLM platforms,” as a well-crafted prompt can still enable malicious behaviour.

At the very least, those concerned about their online safety should limit their use of unsanctioned LLM services.

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