libvpx vulnerability

[zoff99]

make sure libvpx is compiled with correct options.
see:

https://launchpad.net/ubuntu/+source/libvpx/+changelog

https://security-tracker.debian.org/tracker/CVE-2017-0641

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-1258

not sure if only VP9 is affected, so better be safe than sorry

[robinlinden]

It says in https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-1258 that this only applies to VP9 video data.