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CVE-2020-16969: Microsoft Exchange Information Disclosure Vulnerability

• Severity: medium (CVSS 4.3 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-10-16 · updated 2026-06-17

Description

<p>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.</p> <p>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.</p> <p>The security update corrects the way that Exchange handles these token validations.</p>

Affected products

• Microsoft Exchange Server: 2013-cumulative_update_23, 2016-cumulative_update_17, 2016-cumulative_update_18, 2019-cumulative_update_6, 2019-cumulative_update_7
• Microsoft Exchange Server 2013 Cumulative Update 23: from 15.00.0 before publication — fixed in publication
• Microsoft Exchange Server 2016 Cumulative Update 17: from 15.01.0 before publication — fixed in publication
• Microsoft Exchange Server 2016 Cumulative Update 18: from 15.01.0 before publication — fixed in publication
• Microsoft Exchange Server 2019 Cumulative Update 6: from 15.02.0 before publication — fixed in publication
• Microsoft Exchange Server 2019 Cumulative Update 7: from 15.02.0 before publication — fixed in publication

How to fix

Upgrade to a fixed version: Microsoft Exchange Server 2013 Cumulative Update 23 publication; Microsoft Exchange Server 2016 Cumulative Update 17 publication; Microsoft Exchange Server 2016 Cumulative Update 18 publication; Microsoft Exchange Server 2019 Cumulative Update 6 publication; Microsoft Exchange Server 2019 Cumulative Update 7 publication. Check the vendor advisory for mitigations.

References

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-16969
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-16969

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