This is the natural consequence of building everything around "the agent needs access to everything to be useful." The more capabilities you hand an agent, the larger the attack surface when it encounters a malicious page.
The simplest mitigation is also the least popular one: don't give the agent credentials in the first place. Scope it to read-only where possible, and treat every page it visits as untrusted input. But that limits what agents can do, which is why nobody wants to hear it.
The simplest mitigation is also the least popular one: don't give the agent credentials in the first place. Scope it to read-only where possible, and treat every page it visits as untrusted input. But that limits what agents can do, which is why nobody wants to hear it.