Memory corruption exploits continue to plague high profile applications such as web browsers, high performance servers, and mobile devices. Modern defenses for these targets have rendered classic attack vectors that execute shellcode directly on the stack impotent and obsolete. Instead, modern exploits frequently corrupt the data structures found in a program’s memory allocator in order to take control of running processes. These attacks against the heap are much harder to defend against versus classic stack-based buffer overflows because they often rely on an allocator acting on corrupted data in order to take control of a process. In this work, we introduce MPKAlloc, a memory allocator that utilizes memory protection keys (MPKs) found in recent Intel CPUs to effectively isolate heap meta-data from adversaries. We present our prototype implementation of MPKAlloc which hardens the tcmalloc and PartitionAlloc memory allocators used by the popular Chrome web browser. MPKAlloc protects each page containing heap meta-data with a key that provides an allocator exclusive access to the page. Effectively, MPKAlloc thwarts an adversary’s ability to access or corrupt heap meta-data at the hardware level. We embed the MPKAlloc defense in the open-source Chromium web browser, and demonstrate MPKAlloc stopping realistic attack vectors. Furthermore, we evaluate the performance overhead of Chromium configured with MPKAlloc on the top 50 web sites contained in the Alexa site ranking. Our evaluation shows that MPKAlloc introduces a geometric mean of 1.71% performance overhead (2.44% on average) when browsing the most popular web sites, in exchange for a significant increase in security against heap meta-data exploitation.