A use after free in Blink in Google Chrome prior to 57.0.2987.133 for Linux, Windows, and Mac, and 57.0.2987.132 for Android, allowed a remote attacker to perform an out of bounds memory read via a crafted HTML page.
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.