  QCD sum rules are evaluated at finite nucleon densities and temperatures to
determine the change of mass parameters for the lightest vector mesons $\rho$,
$\omega$ and $\phi$ in a strongly interacting medium. For conditions relevant
for the starting experiments at HADES we find that the in-medium mass shifts of
the $\rho$ and $\omega$ mesons are governed, within the Borel QCD sum rule
approach, by the density and temperature dependence of the four-quark
condensate. In particular, the variation of the strength of the density
dependence of the four-quark condensate reflects directly the decreasing mass
of the $\rho$ meson and can lead to a change of the sign of the $\omega$ meson
mass shift as a function of the density. In contrast, the in-medium mass of the
$\phi$ meson is directly related to the chiral strange quark condensate which
seems correspondingly accessible.
