KnowBe4 incident
Defend | Emails Not Being Rendered in Classic Outlook
Resolved on September 8, 2026.
On Septermber 8th we made aware that inbound HTML emails rendered partially or blank in Classic Outlook due to a routine HTML library upgrade in Defend's harmful-code-removal engine interacting with Classic Outlook's legacy Word rendering engine. New Outlook and Outlook on the web were unaffected. This was strictly a display issue: no email was delayed, lost, or compromised, and threat detection remained fully active. Engineering has reverted the update to restore normal rendering. If you temporarily disabled harmful-code removal during this window, please re-enable it to ensure complete protection.
Update timeline
- resolved Sep 08, 2026, 07:00 AM UTC
On Septermber 8th we made aware that inbound HTML emails rendered partially or blank in Classic Outlook due to a routine HTML library upgrade in Defend's harmful-code-removal engine interacting with Classic Outlook's legacy Word rendering engine. New Outlook and Outlook on the web were unaffected. This was strictly a display issue: no email was delayed, lost, or compromised, and threat detection remained fully active. Engineering has reverted the update to restore normal rendering. If you temporarily disabled harmful-code removal during this window, please re-enable it to ensure complete protection.
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