WeWorm: AI Researchers Built a Zero-Click WeChat Call Worm in Under Two Weeks
AI-assisted researchers at Calif developed WeWorm, the first zero-click worm capable of spreading through WeChat calls across iOS and Android, in less than two weeks.
Calif has released a demo of WeWorm, a proof-of-concept worm that exploits a memory corruption vulnerability in WeChat's VoIP stack to achieve remote code execution (RCE) without user interaction. The exploit targets both iOS and Android devices, requiring only an incoming call from a contact on the victim's friend list to hijack the WeChat account. The attack chain allows the compromised device to automatically call other contacts, propagating the worm autonomously. Researchers demonstrated the full cycle using three devices: a Pixel 10a attacker, an iPhone 17e victim, and a second Pixel 10a secondary victim. The initial RCE exploit was written in approximately two days with AI assistance, while the complete worm logic required one additional week.
The vulnerability grants attackers full control over the WeChat application, enabling message interception, outgoing calls, and account impersonation. When chained with other reported bugs, the exploit can lead to full device compromise. Crucially, the attack succeeds even if the victim declines the call or does not interact with the phone, provided the attacker remains on the friend list. Calif notes that while sophisticated actors have long possessed such capabilities, the integration of AI tools significantly lowers the barrier to entry, allowing less skilled groups to develop complex worms rapidly. The team emphasized that the speed of discovery and patching also benefits defenders, citing their own timeline from discovery to mitigation.
Tencent received the bug report on July 24 and released mitigating updates (Android 8.0.77 and iOS 8.0.76) by August 21. Full server-side mitigation for all users was confirmed on August 28. Technical details regarding the specific memory corruption issue remain withheld pending a future conference presentation. Calif intends to continue researching unconventional attack surfaces in messaging apps, advocating for industry-wide collaboration between governments and private sectors to leverage AI for defensive security measures rather than restricting its development.