Coder AgentAPI exposed user chat history via a DNS rebinding attack

Summary

AgentAPI prior to version 0.4.0 was susceptible to a client-side DNS rebinding attack when hosted over plain HTTP on localhost.

Impact

An attacker could have gained access to the /messages endpoint served by the Agent API. This allowed for the unauthorized exfiltration of sensitive user data, specifically local message history, which could've included secret keys, file system contents, and intellectual property the user was working on locally.

Remediation

We've implemented an Origin and Host header validating middleware and set a secure by default configuration.

Please upgrade to version 0.4.0 or later.

Credits

We'd like to thank Evan Harris from mcpsec.dev for reporting this issue and following the coordinated disclosure policy.