Mozilla security engineer David Keeler reported that when an overridable error is encountered, such as those for expired certificates or a host name does not match a certificate, pinning checks can be be skipped. This would allow for a user to override a pinned certificate when they should not be able to do so. This issue does not allow for third parties to cause a certificate to be overridden and the user would still have to manually do so.

In general this flaw cannot be exploited through email in the Thunderbird product because scripting is disabled, but is potentially a risk in browser or browser-like contexts.



External Reference:

http://www.mozilla.org/security/announce/2015/mfsa2015-67.html


Acknowledgements:

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