Security researcher Muneaki Nishimura discovered a flaw in the Mozilla's HTTP Alternative Services implementation. If an Alt-Svc header is specified in the HTTP/2 response, SSL certificate verification can be bypassed for the specified alternate server. As a result of this, warnings of invalid SSL certificates will not be displayed and an attacker could potentially impersonate another site through a man-in-the-middle (MTIM), replacing the original certificate with their own. 


External Reference:

http://www.mozilla.org/security/announce/2015/mfsa2015-44.html


Acknowledgements:

Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Muneaki Nishimura as the original reporter.

Statement:

This issue does not affect the version of firefox and thunderbird as shipped with Red Hat Enterprise Linux 5, 6 and 7.