Out-of-bounds write in Napoca BIOS INT 0x15 E820 memory map handler (VA-13905)

Summary

Bitdefender Napoca bare-metal hypervisor contains an out-of-bounds write vulnerability in the BIOS INT 0x15 / E820 memory map handler, implemented in napoca/guests/bios_handlers.c. The handler computes a destination offset into the guest RealModeMemory buffer from guest-controlled ES and EDI register values without validating that the resulting address remains within the 1MB RealModeMemory allocation. A malicious guest operating in real mode can trigger the issue by invoking INT 0x15 with AX=0xE820, EDX=0x534D4150, ECX greater than or equal to 20, EBX=0, ES=0xFFFF, and EDI=0xFFFF. This can cause a write of up to 20 bytes past the end of the RealModeMemory buffer into the hypervisor heap. The product is end-of-life and unsupported when assigned.