Cybersecurity researchers have discovered a vulnerability in a Chrome extension linked to Anthropic’s Claude AI assistant that could allow attackers to hijack AI agent sessions and execute unauthorized actions. The issue highlights growing security concerns surrounding browser-based AI assistants and extensions integrated with sensitive workflows.
According to researchers from ExtensionTotal, the vulnerability affected the “Claude for Chrome” extension and involved weaknesses in how the extension handled communication between webpages and the AI agent. Attackers could reportedly exploit the flaw by injecting malicious scripts into websites visited by the victim, enabling unauthorized commands to be sent to the Claude extension in the background.
Researchers explained that the vulnerability stemmed from insufficient validation of postMessage events, a browser communication mechanism often used between webpages and extensions. By abusing this behavior, malicious websites could interact with the extension as if they were trusted sources. This could potentially allow attackers to manipulate prompts, access AI-generated content, or trigger actions performed by the AI agent.
The report warned that successful exploitation could expose sensitive enterprise data processed through the AI assistant, including emails, documents, code snippets, credentials, and browser session information. In environments where AI agents are integrated with productivity tools or automation workflows, attackers could potentially escalate access and perform broader malicious operations.
Anthropic was reportedly informed about the vulnerability and has since addressed the issue through an updated extension release. Researchers stated that the fix included stricter origin validation and improved controls around message handling between webpages and the extension. Users were advised to update the extension immediately to receive the security patch.
Security experts noted that the incident demonstrates how browser extensions connected to AI systems can significantly expand attack surfaces. As AI assistants gain deeper integration with browsers, enterprise platforms, and automation tools, vulnerabilities in extension permissions and inter-process communication mechanisms could become increasingly valuable targets for attackers.
