A vulnerability in the GPU kernel allows it to read sensitive data from another GPU kernel, even from another user or application, through an optimized GPU memory region called local memory . This issue can be exploited to extract data from the local memory of a GPU, potentially revealing confidential information. The vulnerability, known as LeftoverLocals, is particularly concerning in multi-user systems where different users' handlers run on the same GPU. It can also be used in malicious software to track the activity of processes running on the GPU. The estimated number of potentially affected devices worldwide is not specified, but it is mentioned that the issue affects millions of devices, including iPhones, iPads, and Macs.