WhatsApp Vulnerability Exposes Phone Numbers of 3.5 Billion Users
Posted: Thu Nov 20, 2025 3:36 pm
Security researchers from the University of Vienna have uncovered a critical vulnerability in WhatsApp that allowed them to enumerate phone numbers of 3.5 billion users worldwide, exposing a massive privacy flaw in the world’s most popular messaging platform.
The security flaw stems from WhatsApp’s contact discovery mechanism, which enables users to check if their contacts are registered on the platform.
Researchers exploited weak rate-limiting protections to probe over 100 million phone numbers per hour without encountering blocking or effective rate-limiting measures.
Using reverse-engineered WhatsApp APIs, the team systematically queried 63 billion candidate phone numbers across 245 countries between December 2024 and April 2025.
https://cyberpress.org/whatsapp-vulnerability/
The security flaw stems from WhatsApp’s contact discovery mechanism, which enables users to check if their contacts are registered on the platform.
Researchers exploited weak rate-limiting protections to probe over 100 million phone numbers per hour without encountering blocking or effective rate-limiting measures.
Using reverse-engineered WhatsApp APIs, the team systematically queried 63 billion candidate phone numbers across 245 countries between December 2024 and April 2025.
https://cyberpress.org/whatsapp-vulnerability/