I performed a security analysis of Zoom and reported two vulnerabilities. One was a buffer overflow that affected both Zoom clients and MMR servers, and one was an info leak that is only useful to attackers on MMR servers. Both of these vulnerabilities were fixed on November 24, 2021.
The vulnerabilities in Zoom’s MMR server are especially concerning, as this server processes meeting audio and video content, so a compromise could allow an attacker to monitor any Zoom meetings that do not have end-to-end encryption enabled. While I was not successful in exploiting these vulnerabilities, I was able to use them to perform many elements of exploitation, and I believe that an attacker would be able to exploit them with sufficient investment. The lack of ASLR in the Zoom MMR process greatly increased the risk that an attacker could compromise it, and it is positive that Zoom has recently enabled it. That said, if vulnerabilities similar to the ones that I reported still exist in the MMR server, it is likely that an attacker could bypass it, so it is also important that Zoom continue to improve the robustness of the MMR code.
It is also important to note that this research was possible because Zoom allows customers to set up their own servers, meanwhile no other video conferencing solution with proprietary servers that I have investigated allows this, so it is unclear how these results compare to other video conferencing platforms.
Overall, while the client bugs that were discovered during this research were comparable to what Project Zero has found in other videoconferencing platforms, the server bugs were surprising, especially when the server lacked ASLR and supports modes of operation that are not end-to-end encrypted.
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