Code: tight_filter_gradient24(VncState *vs, uint8_t *buf, int w, int h)
{
    uint32_t *buf32;
    uint32_t pix32;
    int shift[3];
    int *prev;
    int here[3], upper[3], left[3], upperleft[3];
    int prediction;
    int x, y, c;

     buf32 = (uint32_t *)buf;
     memset(vs->tight.gradient.buffer, 0, w * 3 * sizeof(int));
 
    if ((vs->clientds.flags & QEMU_BIG_ENDIAN_FLAG) ==
        (vs->ds->surface->flags & QEMU_BIG_ENDIAN_FLAG)) {
        shift[0] = vs->clientds.pf.rshift;
        shift[1] = vs->clientds.pf.gshift;
        shift[2] = vs->clientds.pf.bshift;
     } else {
        shift[0] = 24 - vs->clientds.pf.rshift;
        shift[1] = 24 - vs->clientds.pf.gshift;
        shift[2] = 24 - vs->clientds.pf.bshift;
     }
 
     for (y = 0; y < h; y++) {
        for (c = 0; c < 3; c++) {
            upper[c] = 0;
            here[c] = 0;
        }
        prev = (int *)vs->tight.gradient.buffer;
        for (x = 0; x < w; x++) {
            pix32 = *buf32++;
            for (c = 0; c < 3; c++) {
                upperleft[c] = upper[c];
                left[c] = here[c];
                upper[c] = *prev;
                here[c] = (int)(pix32 >> shift[c] & 0xFF);
                *prev++ = here[c];

                prediction = left[c] + upper[c] - upperleft[c];
                if (prediction < 0) {
                    prediction = 0;
                } else if (prediction > 0xFF) {
                    prediction = 0xFF;
                }
                *buf++ = (char)(here[c] - prediction);
            }
        }
    }
}

Vulnerability Type: 
CWE ID: CWE-125
Summary: An out-of-bounds memory access issue was found in Quick Emulator (QEMU) before 1.7.2 in the VNC display driver. This flaw could occur while refreshing the VNC display surface area in the 'vnc_refresh_server_surface'. A user inside a guest could use this flaw to crash the QEMU process.
Commit Message: 