CVE-2021-27921, CVE-2021-27922, CVE-2021-27923: Fix DOS attacks#

There is an exhaustion of memory DOS attack in BLP, ICNS, ICO images where Pillow did not properly check the reported size of the contained image. These images could cause arbitrarily large memory allocations.

These issues were reported by Jiayi Lin, Luke Shaffer, Xinran Xie and Akshay Ajayan of Arizona State University.