static int cirrus_vga_read_sr(CirrusVGAState * s)
{
    switch (s->vga.sr_index) {
    case 0x00:			// Standard VGA
    case 0x01:			// Standard VGA
    case 0x02:			// Standard VGA
    case 0x03:			// Standard VGA
    case 0x04:			// Standard VGA
	return s->vga.sr[s->vga.sr_index];
    case 0x06:			// Unlock Cirrus extensions
	return s->vga.sr[s->vga.sr_index];
    case 0x10:
    case 0x30:
    case 0x50:
    case 0x70:			// Graphics Cursor X
    case 0x90:
    case 0xb0:
    case 0xd0:
    case 0xf0:			// Graphics Cursor X
	return s->vga.sr[0x10];
    case 0x11:
    case 0x31:
    case 0x51:
    case 0x71:			// Graphics Cursor Y
    case 0x91:
    case 0xb1:
    case 0xd1:
    case 0xf1:			// Graphics Cursor Y
	return s->vga.sr[0x11];
    case 0x05:			// ???
    case 0x07:			// Extended Sequencer Mode
    case 0x08:			// EEPROM Control
    case 0x09:			// Scratch Register 0
    case 0x0a:			// Scratch Register 1
    case 0x0b:			// VCLK 0
    case 0x0c:			// VCLK 1
    case 0x0d:			// VCLK 2
    case 0x0e:			// VCLK 3
    case 0x0f:			// DRAM Control
    case 0x12:			// Graphics Cursor Attribute
    case 0x13:			// Graphics Cursor Pattern Address
    case 0x14:			// Scratch Register 2
    case 0x15:			// Scratch Register 3
    case 0x16:			// Performance Tuning Register
    case 0x17:			// Configuration Readback and Extended Control
    case 0x18:			// Signature Generator Control
    case 0x19:			// Signal Generator Result
    case 0x1a:			// Signal Generator Result
    case 0x1b:			// VCLK 0 Denominator & Post
    case 0x1c:			// VCLK 1 Denominator & Post
    case 0x1d:			// VCLK 2 Denominator & Post
    case 0x1e:			// VCLK 3 Denominator & Post
    case 0x1f:			// BIOS Write Enable and MCLK select
#ifdef DEBUG_CIRRUS
	printf("cirrus: handled inport sr_index %02x\n", s->vga.sr_index);
#endif
	return s->vga.sr[s->vga.sr_index];
    default:
#ifdef DEBUG_CIRRUS
	printf("cirrus: inport sr_index %02x\n", s->vga.sr_index);
#endif
	return 0xff;
	break;
    }
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.