Mesh Messaging in Large-scale Protests: Breaking Bridgefy

Mesh messaging applications allow users in relative proximity to communicate without the Internet. The most viable offering in this space, Bridgefy, has recently seen increased uptake in areas experiencing large-scale protests (Hong Kong, India, Iran, US, Zimbabwe, Belarus, Thailand), suggesting its use in these protests. It is also being promoted as a communication tool for use in such situations by its developers and others. In this work, we perform a security analysis of Bridgefy. Our results show that Bridgefy permits its users to be tracked, offers no authenticity, no effective confidentiality protections and lacks resilience against adversarially crafted messages. We verify these vulnerabilities by demonstrating a series of practical attacks on Bridgefy. Thus, if protesters rely on Bridgefy, an adversary can produce social graphs about them, read their messages, impersonate anyone to anyone and shut down the entire network with a single maliciously crafted message. As a result, we conclude that participants of protests should avoid relying on Bridgefy until these vulnerabilities are addressed and highlight the resulting gap in the design space for secure messaging applications.