AIKIDO-2026-370504

TL;DR

libheif holds a non-recursive per item decode mutex across nested decodes and decodes grid tiles in parallel. A crafted file whose tiles reference each other through alpha auxiliary edges makes two worker threads acquire the same item mutexes in opposite order, producing a permanent deadlock that the per path cycle guard cannot detect across threads. This hangs decoding of a malformed grid image. The fix rejects cyclic decode reference graphs before any decoding begins.