ChatGPT previews opened a route to data theft and phishing
Check Point Research found that ChatGPT’s HTML previews, added to code blocks in February 2026, could bypass Lockdown Mode and expose users to silent chat-data theft and phishing.
An attacker could deliver crafted HTML through a malicious prompt, GPT, or shared chat. When ChatGPT rendered the preview, the content could get around the mode’s network limits and send conversation data to an external server. The vulnerability could also manipulate ChatGPT Classic’s interface to show arbitrary pop-ups, creating a phishing surface.
Lockdown Mode is therefore less like an isolation boundary than a set of restrictions on network paths: if users process untrusted content in sensitive sessions, the interface displaying it can itself become a route to data exposure.
ChatGPT Lockdown Mode Bypass: Phishing, Malware Delivery, and Silent Data Exfiltration - Check Point Research
Research by: Alexey Bukhteyev Key Takeaways Introduction Earlier this year, Check Point Research disclosed a security flaw in ChatGPT’s code-execution runtime that allowed sensitive conversation data to be silently exfiltrated to an attacker-controlled server through DNS tunneling, a hidden outbound channel that bypassed the runtime’s network isolation.