Yesterday, Microsoft released a new security update for Exchange Server 2013, 2016 and 2019. The update closes the vulnerability CVE-2020-16969. The vulnerability can be exploited with a specially crafted email, so the update should be installed promptly. The update is classified as "Important".
Microsoft describes the vulnerability as follows:
An information disclosure vulnerability exists in how Microsoft Exchange validates tokens when handling certain messages. An attacker who successfully exploited the vulnerability could use this to gain further information from a user.
To exploit the vulnerability, an attacker could include specially crafted OWA messages that could be loaded, without warning or filtering, from the attacker-controlled URL. This callback vector provides an information disclosure tactic used in web beacons and other types of tracking systems.
The security update corrects the way that Exchange handles these token validations.
Source: https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/CVE-2020-16969
The update can be downloaded here:
- Microsoft Exchange Server 2013 Cumulative Update 23
- Microsoft Exchange Server 2013 Cumulative Update 17
- Microsoft Exchange Server 2016 Cumulative Update 18
- Microsoft Exchange Server 2019 Cumulative Update 6
- Microsoft Exchange Server 2019 Cumulative Update 7
As always, updates should be tested before installation. The update is already delivered with Windows Update.
