xmonad-contrib is a set of third party tiling algorithms, configurations, and scripts for xmonad.
A vulnerability in the Xmonad.Hooks.DynamicLog module could allow a malicious website with a specially crafted title to inject commands into the title bar which would be executed when the bar is clicked.
A remote attacker could possibly execute arbitrary code with the privileges of the process or cause a Denial of Service condition.
There is no known workaround at this time.
All xmonad-contrib users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=x11-wm/xmonad-contrib-0.11.2"