Microsoft released a new security update for Exchange Server 2016 and 2019 yesterday. The update closes a vulnerability classified as "Important".
Description of the vulnerability:
A cross-site scripting (XSS) vulnerability exists when Microsoft Exchange Server does not properly sanitize a specially crafted web request to an affected Exchange server. An authenticated attacker could exploit the vulnerability by sending a specially crafted request to an affected server.
The attacker who successfully exploited the vulnerability could then perform cross-site scripting attacks on affected systems and run script in the security context of the current user. The attacks could allow the attacker to read content that the attacker is not authorized to read, use the victim’s identity to take actions on the Exchange server on behalf of the user, such as change permissions and delete content, and inject malicious content in the browser of the user.
The security update addresses the vulnerability by helping to ensure that Exchange Server properly sanitizes web requests.
Source: https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/CVE-2020-0903
Although no exploit for the vulnerability is yet known, this was not long in coming with the last vulnerability. The update should therefore be installed promptly.
Click here to download the updates directly:
- Download Security Update For Exchange Server 2019 Cumulative Update 4 (KB4540123)
- Download Security Update For Exchange Server 2019 Cumulative Update 3 (KB4540123)
- Download Security Update For Exchange Server 2016 Cumulative Update 15 (KB4540123)
- Download Security Update For Exchange Server 2016 Cumulative Update 14 (KB4540123)
Here is another article with known problems with this update, this article should definitely be read before installation:
The security update is already being distributed via Windows Update and can therefore also be installed via WSUS. However, the update should be tested beforehand. The last update apparently caused problems in some environments.
