Avast! - Out-of-Bounds Write Decrypting PEncrypt Packed executables

Source: https://code.google.com/p/google-security-research/issues/detail?id=554

The attached PEncrypt packed executable causes an OOB write on Avast Server Edition. 

(gdb) bt
#0  0xf6f5e64a in EmulatePolyCode(_POLY_INFO*, int) () from /proc/self/cwd/defs/15092301/engine.so
#1  0xf6f7d334 in pencryptMaybeUnpack(CFMap&, _PEEXE_INFO*, asw::root::CGenericFile*, _EXE_UNPACK_INFO*) () from /proc/self/cwd/defs/15092301/engine.so
#2  0xf6f75805 in CPackWinExec::packIsPacked(CFMap&, void**, ARCHIVE_UNPACKING_INFO*) () from /proc/self/cwd/defs/15092301/engine.so
#3  0xf6e8d1a2 in CAllPackers::IsPacked(CFMap&, _SARCHIVERANGE*, unsigned int, unsigned int, unsigned int, unsigned int, CObjectName const*, unsigned int*, unsigned int*, _PEEXE_INFO**) () from /proc/self/cwd/defs/15092301/engine.so
#4  0xf6e784ef in CScanInfo::ProcessPackingReal(CObjectName&, CFMap&, _VIRUSDATAARRAY*, int&, unsigned int) () from /proc/self/cwd/defs/15092301/engine.so
#5  0xf6e78bdd in CScanInfo::ProcessPacking(CObjectName&, unsigned int, unsigned int) () from /proc/self/cwd/defs/15092301/engine.so
#6  0xf6e74fbd in CScanInfo::ProcessArea(CObjectName&, unsigned int, unsigned int) () from /proc/self/cwd/defs/15092301/engine.so
#7  0xf6e752af in CScanInfo::ProcessTopArea(CObjectName&, unsigned int) () from /proc/self/cwd/defs/15092301/engine.so
#8  0xf6e7d6db in avfilesScanRealMulti () from /proc/self/cwd/defs/15092301/engine.so
#9  0xf6e81915 in avfilesScanReal () from /proc/self/cwd/defs/15092301/engine.so
#10 0x0805d2a5 in avfilesScanReal ()
#11 0x0805498c in engine_scan ()
(gdb) x/i $pc
=> 0xf6f5e64a <_Z15EmulatePolyCodeP10_POLY_INFOi+7194>:	mov    WORD PTR [edx],ax
(gdb) p/x $edx
$7 = 0xe73f181f
(gdb) p/x $ax
$8 = 0x1060

Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/38931.zip