When performing a symlink lookup from a reiserfs filesystem, grub's reiserfs fs module uses user-controlled parameters from the filesystem geometry to determine the internal buffers size, however it misses to properly check for integer overflows. A maliciouly crafted filesystem may lead some of those buffer size calculation to overflow, causing it to perform a grub_malloc() operation with a smaller size than expected. As a result the grub_reiserfs_read_symlink() will call grub_reiserfs_read_real() with a overflown length parameter leading to a heap based out-of-bounds write during data reading. This flaw may be leveraged to corrupt grub's internal critical data and may result in arbitrary code
execution by-passing secure boot protections.