Opera is a multi-platform web browser.
Peter Zelezny discovered that the shell script used to launch Opera parses shell commands that are enclosed within backticks in the URL provided via the command line.
A remote attacker could exploit this vulnerability by enticing a user to follow a specially crafted URL from a tool that uses Opera to open URLs, resulting in the execution of arbitrary commands on the targeted machine.
There is no known workaround at this time.
All Opera users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=www-client/opera-8.51"