The dominant electroweak production mechanism for single top quarks is the $t$-channel and it features a tWq vertex where q stands for b, s, or d quarks both in production and in the decay of the top quark. For this reason its cross section and branching fractions are sensitive to the strength of the electroweak coupling, making it a suitable channel for direct measurements of the magnitude of Cabibbo-Kobayashi-Maskawa (CKM) matrix elements $|V_{\mathrm{tb}}|$, $|V_{\mathrm{ts}}|$, and $|V_{\mathrm{td}}|$. A precise determination of the magnitude of these parameters of the standard model (SM) of particle physics allows to search for hints of potential contributions from new phenomena beyond the SM. \newline
This poster presents the first direct measurement of the CKM matrix elements $|V_{\mathrm{tb}}|$, $|V_{\mathrm{ts}}|$, and $|V_{\mathrm{td}}|$, making use of single top quark $t$-channel events in proton-proton collision data with a centre-of-mass energy of 13 TeV, collected with the CMS experiment at the LHC. The subset of data analysed corresponds to an integrated luminosity of 35.89 fb$^{-1}$.