The vulnerability was discovered by Tavis Ormandy a well known security researcher and privately reported to Cisco which was patched on Monday January 23rd, 2017. The seriousness of the issue was the seemingly trivial exploitation vector.
“All that’s required for a malicious or compromised website to exploit the vulnerability is to host a file or other resource that contains the string “cwcsf-nativemsg-iframe-43c85c0d-d633-af5e-c056-32dc7efc570b.html” in its URL. That’s a “magic” pattern the WebEx service uses to remotely start a meeting on visiting computers that have the Chrome extension installed.”
If you haven’t done so, UPDATE or UNINSTALL the WebEx extension to remove the vulnerability. More information on the patch can be found here: Cisco Security Advisory
Kudos to Cisco on producing a patch in two days!