CVE-2026-88373: NULL Pointer Dereference

libde265 commit 4d45a6b contains a NULL pointer dereference vulnerability in the NAL parsing path. When de265_push_NAL() is called with a zero-length NAL unit, the resulting NAL_unit may retain a NULL backing buffer, which is subsequently passed as the destination argument to memcpy() in NAL_unit::set_data(). Although the copy length is zero, this violates the nonnull requirement of memcpy() and results in undefined behavior, causing process termination in UBSan-instrumented builds and denial of service.