/usr/share/tcltk/tcllib1.18/virtchannel_base/ is in tcllib 1.18-dfsg-3.
This file is owned by root:root, with mode 0o755.
..
/usr/share/tcltk/tcllib1.18/virtchannel_base/cat.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/facade.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/fifo.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/fifo2.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/halfpipe.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/memchan.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/null.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/nullzero.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/pkgIndex.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/random.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/randseed.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/std.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/string.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/textwindow.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/variable.tcl
/usr/share/tcltk/tcllib1.18/virtchannel_base/zero.tcl