Apple has released Safari 15.6.1 for macOS Big Sur and macOS Catalina. It includes a security fix for a WebKit vulnerability that could lead to arbitrary code execution, according to Apple.
The impact of the vulnerability is that processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited. With the Safari 15.6.1 update an An out-of-bounds write issue was addressed with improved bounds checking.