KASAN, the Kernel Address Sanitizer, is a debugging tool built into the Linux kernel that detects memory errors while the kernel is running. It can catch problems such as out-of-bounds reads and writes and use-after-free bugs by checking memory accesses and reporting an error when something touches memory it should not.
Kernel developers and security researchers use KASAN mainly in testing. When a fuzzer or a test triggers a bug, a KASAN report gives a stack trace and details that show where the invalid access happened, which makes bugs much easier to find and fix. Many kernel vulnerabilities have been discovered this way.
KASAN is a diagnostic tool, not a protection for production systems. It slows the kernel and uses extra memory, so it is not normally enabled on production machines. A KASAN report also shows that a memory error occurred, not that the bug can be exploited to gain control, since exploitability depends on what an attacker can influence.
When you see a KASAN report in a bug or advisory, read it as evidence that a memory error exists in a particular code path. To know whether your systems are affected, check the vendor advisory for your kernel version and distribution, and apply the fixed kernel once it is available.