qgis - Sum of values within a buffer polygon

I need to do the following in QGIS and hope so much anyone could help.

I have a vector layer with points. Each point represents a firm with the number of employees in the attribute table. I want to buffer around every point, so that the buffer's attribute table contains the sum of employees within the buffer.

It would be so great if the sum to each point could be written to the attribute table.

Thanks for your help.