tcolorbox: Potential bug with duplicate label for hyperref link

hyperref has a built-in mechanism for this. If for a counter the command \theH<counter> is defined, then it is used for internal anchor names instead of \the<counter>.

\documentclass{scrartcl}
\usepackage{tcolorbox}
\usepackage{hyperref}

\newtcolorbox[auto counter,number within=section]{mybox}[1][]{%
  title=MyBox~\thetcbcounter,
  #1
}
\providecommand{\theHtcbcounter}{\thesection.\arabic{tcbcounter}}

\begin{document}

Mybox~\ref{mybox1}; Mybox~\ref{mybox2}

\clearpage
\section{Section}
\begin{mybox}[label=mybox1]
The counter name is \texttt{\tcbcounter}.
\end{mybox}

\clearpage
\section{Section}
\begin{mybox}[label=mybox2]
The counter name is \texttt{\tcbcounter}.
\end{mybox}
\end{document}

This way the two links will have distinct anchor names and all is well.

If you want this to work with later loading of hyperref, you have to plunge in the internals:

\makeatletter
\providecommand\theHtcb@cnt@mybox{\thesection.\arabic{tcb@cnt@mybox}}
\makeatother

because tcolorbox associates that counter to the color box.