imgproxy 3.3.0 before 4.0.17 contains an out-of-bounds heap read and write in the ICO loader's BMP header reconstruction (vips_foreign_load_ico_header in vips/icoload.c) when an ICO entry declares a tiny data size, causing unvalidated header fields to be read and written past the allocated buffer. Unauthenticated remote attackers can supply a crafted ICO image to corrupt adjacent heap chunk metadata, triggering a glibc abort that crashes the worker.