# CVE-2020-0688: Microsoft Exchange Validation Key Remote Code Execution Vulnerability

CVE-2020-0688 is fixed in 6 products on 1 platform, first by KB4536989, released February 11, 2020. It is being exploited: CISA added it to the Known Exploited Vulnerabilities catalog on November 3, 2021, with known ransomware use. Patch Radar priority: Patch now.

- Web page: https://patchblox.com/security/cve/CVE-2020-0688
- Priority: Patch now
- CVSS: n/a (Important)
- EPSS: 0.9996
- CISA KEV: listed Nov 3, 2021, federal due date May 3, 2022, known ransomware use
- Exploited (vendor report): no
- Publicly disclosed: no
- Vendor exploitability assessment: Exploitation More Likely
- Published: Feb 11, 2020
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2020-0688

## Description

<p>A remote code execution vulnerability exists in Microsoft Exchange Server when the server fails to properly create unique keys at install time.</p> <p>Knowledge of a the validation key allows an authenticated user with a mailbox to pass arbitrary objects to be deserialized by the web application, which runs as SYSTEM.</p> <p>The security update addresses the vulnerability by correcting how Microsoft Exchange creates the keys during install.</p>

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Microsoft | Microsoft Exchange Server 2010 Service Pack 3 Update Rollup 30 |  | [KB4536989](https://patchblox.com/security/data/fix/microsoft/kb4536989.md) | Feb 11, 2020 |
| Microsoft | Microsoft Exchange Server 2013 Cumulative Update 23 |  | [KB4536988](https://patchblox.com/security/data/fix/microsoft/kb4536988.md) | Feb 11, 2020 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 14 |  | [KB4536987](https://patchblox.com/security/data/fix/microsoft/kb4536987.md) | Feb 11, 2020 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 15 |  | [KB4536987](https://patchblox.com/security/data/fix/microsoft/kb4536987.md) | Feb 11, 2020 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 3 |  | [KB4536987](https://patchblox.com/security/data/fix/microsoft/kb4536987.md) | Feb 11, 2020 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 4 |  | [KB4536987](https://patchblox.com/security/data/fix/microsoft/kb4536987.md) | Feb 11, 2020 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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