/usr/share/gimp/2.0/brushes/Circle-15.vbr is in gimp-data 2.6.12-1ubuntu1.4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 | GIMP-VBR
1.0
Circle (15)
20.000000
7.500000
1.000000
1.000000
0.000000
|