A heap-based buffer overflow issue was discovered in UPX in PackTmt::pack() in p_tmt.cpp file. The flow allows an attacker to cause a denial of service (abort) via a crafted file.
https://github.com/upx/upx/issues/632
https://github.com/upx/upx/commit/510505a85cbe45e51fbd470f1aa8b02157c429d4