Mozilla Foundation Security Advisory 2015-67

Key pinning is ignored when overridable errors are encountered

July 2, 2015
David Keeler
Firefox, Firefox ESR, SeaMonkey, Thunderbird
Fixed in
  • Firefox 39
  • Firefox ESR 38.1
  • SeaMonkey 2.35
  • Thunderbird 38.1


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.