TLDR: OpenAI has patched a critical ‘zero-click’ vulnerability, dubbed ‘ShadowLeak’ by cybersecurity firm Radware, in its ChatGPT Deep Research agent. This flaw could have allowed attackers to silently exfiltrate sensitive Gmail data through a sophisticated indirect prompt injection attack, without any user interaction.
Cybersecurity researchers from Radware have uncovered and disclosed a significant ‘zero-click’ vulnerability, codenamed ‘ShadowLeak,’ within OpenAI’s ChatGPT Deep Research agent. This critical flaw had the potential to enable attackers to extract sensitive Gmail inbox data from users without their knowledge or any required interaction.
The Deep Research agent, launched by OpenAI in February 2025, is an advanced agentic capability built into ChatGPT designed to conduct multi-step internet research and generate comprehensive reports. It boasts integrations with various applications, including Gmail, allowing it to analyze personal data and documents for research purposes.
The ‘ShadowLeak’ attack leverages an indirect prompt injection technique. Attackers would send a seemingly innocuous email to a victim, embedding hidden commands within the email’s HTML using methods like white-on-white text, microscopic fonts, or CSS layout tricks. These commands would remain invisible to the user but would be parsed and obeyed by the Deep Research agent.
According to Radware researchers Zvika Babo, Gabi Nakibly, and Maor Uziel, “The attack utilizes an indirect prompt injection that can be hidden in email HTML (tiny fonts, white-on-white text, layout tricks) so the user never notices the commands, but the agent still reads and obeys them.” They further explained the severity of this new class of attack: “Unlike prior research that relied on client-side image rendering to trigger the leak, this attack leaks data directly from OpenAI’s cloud infrastructure, making it invisible to local or enterprise defenses.” This ‘service-side exfiltration’ means the data theft occurs entirely within OpenAI’s cloud environment, with the agent’s autonomous browsing tool executing the exfiltration without any client involvement.
In a proof-of-concept, Radware demonstrated how a threat actor could instruct the Deep Research agent to gather personal information from other messages in the inbox and exfiltrate it to an external server. The researchers crafted a prompt that explicitly instructed the agent to use the `browser.open()` tool with a malicious URL, encoding the extracted Personally Identifiable Information (PII) into Base64 format before appending it to the URL, disguised as a ‘security measure’ during transmission.
Radware responsibly disclosed their findings to OpenAI via the Bugcrowd platform on June 18, 2025. OpenAI addressed the issue in early August, and by early September, they acknowledged the vulnerability and marked it as resolved. This swift action by OpenAI prevented any known exploitation of the flaw, mitigating potential widespread data breaches.
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The incident highlights the evolving landscape of AI security, particularly with the rise of autonomous AI agents capable of interacting with personal data and external services. It underscores the importance of robust security measures and continuous monitoring of AI systems to prevent sophisticated attacks like ‘ShadowLeak’ that exploit the backend execution capabilities of these advanced models.
