Vulnerability Instance

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.