  We present a strong lensing system, composed of 4 multiple images of a source
at z = 2.387, created by two lens galaxies, G1 and G2, belonging to the galaxy
cluster MACS J1115.9+0129 at z = 0.353. We use observations taken as part of
the Cluster Lensing and Supernova survey with Hubble, CLASH, and its
spectroscopic follow-up programme at the Very Large Telescope, CLASH-VLT, to
estimate the total mass distributions of the two galaxies and the cluster
through strong gravitational lensing models. We find that the total projected
mass values within the half-light radii, R_{e}, of the two lens galaxies are
M_{T,G1}(< R_{e,G1}) = (3.6 +/- 0.4) x 10^{10}M_{Sun} and M_{T,G2}(< R_{e,G2})
= (4.2 +/- 1.6) x 10^{10}M_{Sun}. The effective velocity dispersion values of
G1 and G2 are (122 +/- 7) km/s and (137 +/- 27) km/s, respectively. We remark
that these values are relatively low when compared to those of ~200-300 km/s,
typical of lens galaxies found in the field by previous surveys. By fitting the
spectral energy distributions of G1 and G2, we measure projected luminous over
total mass fractions within R_{e} of 0.11 +/- 0.03, for G1, and 0.73 +/- 0.32,
for G2. The fact that the less massive galaxy, G1, is dark-matter dominated in
its inner regions raises the question of whether the dark matter fraction in
the core of early-type galaxies depends on their mass. Further investigating
strong lensing systems will help us understand the influence that dark matter
has on the structure and evolution of the inner regions of galaxies.
