--- title: "CVE-2021-26855: Microsoft Exchange Server Remote Code… | CubePath" description: "Microsoft Exchange Server Remote Code Execution Vulnerability" language: en source: https://cubepath.com/security/cve/CVE-2021-26855 --- # CVE-2021-26855: Microsoft Exchange Server Remote Code… | CubePath ## Description Microsoft Exchange Server Remote Code Execution Vulnerability Official description from the CVE record, published by microsoft. Copyright © 1999-2026 The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CVE license. [View the record on cve.org](https://www.cve.org/CVERecord?id=CVE-2021-26855) ## Key data ### CVSS 3.1 Critical 9.1 Score published by microsoft in the CVE record. CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:F/RL:O/RC:C | Metric | Value | What it means | | ---------------------- | --------- | ----------------------------------------------------------------------------------- | | Attack vector | Network | The vulnerable component can be reached over a network, possibly from the Internet. | | Attack complexity | Low | No special conditions are needed. The attack can be repeated at will. | | Privileges required | None | No account or privileges are needed. | | User interaction | None | No action from any user is needed. | | Scope | Unchanged | The impact stays within the vulnerable component. | | Confidentiality impact | High | Serious or total effect on the secrecy of data. | | Integrity impact | High | Serious or total effect on the trustworthiness of data. | | Availability impact | None | No effect on availability. | CVSS is owned and managed by FIRST.Org, Inc. (FIRST) and is used by permission. Each CVSS score on this site is shown together with its vector string, as published in the CVE record by the source named next to it. Learn more at [first.org/cvss](https://www.first.org/cvss/) . ### EPSS Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days. Score 0.99996 (99.99% probability) Percentile 99.98% Scores of Nov 10, 2026 Model v2026.06.15 ### CISA Known Exploited Vulnerabilities This CVE is listed in the CISA KEV catalog. Name in the catalog Microsoft Exchange Server Remote Code Execution Vulnerability Added to the catalog Nov 3, 2021 Federal due date May 3, 2022 Ransomware campaigns Known use ### CISA assessment as of Mar 1, 2021 Stakeholder-Specific Vulnerability Categorization (SSVC) decision points added by CISA. Exploitation Recorded by CISA as active Automatable yes Technical impact total ### Weakness (CWE) CWE catalog version 5.0. CWE names: Copyright © 2006-2026, The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CWE license. - [CWE-918](https://cwe.mitre.org/data/definitions/918.html) Server-Side Request Forgery ## Affected products Products listed in the CVE record, as the CNA published them. - Microsoft Exchange Server 2013 Cumulative Update 21 - affected: 15.00.0 up to before 15.00.1395.012 - Microsoft Exchange Server 2013 Cumulative Update 22 - affected: 15.00.0 up to before 15.00.1473.006 - Microsoft Exchange Server 2013 Cumulative Update 23 - affected: 15.00.0 up to before 15.00.1497.012 - Microsoft Exchange Server 2016 Cumulative Update 10 - affected: 15.01.0 up to before 15.01.1531.012 - Microsoft Exchange Server 2016 Cumulative Update 11 - affected: 15.01.0 up to before 15.01.1591.018 - Microsoft Exchange Server 2016 Cumulative Update 12 - affected: 15.01.0 up to before 15.01.1713.010 - Microsoft Exchange Server 2016 Cumulative Update 13 - affected: 15.01.0 up to before 15.01.1779.008 - Microsoft Exchange Server 2016 Cumulative Update 14 - affected: 15.01.0 up to before 15.01.1847.012 - Microsoft Exchange Server 2016 Cumulative Update 15 - affected: 15.01.0 up to before 15.01.1913.012 - Microsoft Exchange Server 2016 Cumulative Update 16 - affected: 15.01.0 up to before 15.01.1979.008 - Microsoft Exchange Server 2016 Cumulative Update 17 - affected: 15.01.0 up to before 15.01.2044.013 - Microsoft Exchange Server 2016 Cumulative Update 18 - affected: 15.01.0 up to before 15.01.2106.013 - Microsoft Exchange Server 2016 Cumulative Update 19 - affected: 15.01.0 up to before 15.01.2176.009 - Microsoft Exchange Server 2016 Cumulative Update 8 - affected: 15.01.0 up to before 15.01.1415.010 - Microsoft Exchange Server 2016 Cumulative Update 9 - affected: 15.01.0 up to before 15.01.1466.016 - Microsoft Exchange Server 2019 - affected: 15.02.0 up to before 15.02.0221.018 - Microsoft Exchange Server 2019 Cumulative Update 1 - affected: 15.02.0 up to before 15.01.1979.006 - Microsoft Exchange Server 2019 Cumulative Update 2 - affected: 15.02.0 up to before 15.02.0397.011 - Microsoft Exchange Server 2019 Cumulative Update 3 - affected: 15.02.0 up to before 15.02.0464.015 - Microsoft Exchange Server 2019 Cumulative Update 4 - affected: 15.02.0 up to before 15.02.0659.012 - Microsoft Exchange Server 2019 Cumulative Update 5 - affected: 15.02.0 up to before 15.02.0595.008 - Microsoft Exchange Server 2019 Cumulative Update 6 - affected: 15.02.0 up to before 15.02.0529.013 - Microsoft Exchange Server 2019 Cumulative Update 7 - affected: 15.02.0 up to before 15.02.0721.013 - Microsoft Exchange Server 2019 Cumulative Update 8 - affected: 15.02.0 up to before 15.02.0792.010 ## References Links listed in the CVE record. They lead to other sites, which CubePath does not control. - [Microsoft Exchange Server Remote Code Execution Vulnerability](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26855) (msrc.microsoft.com) vendor-advisory patch - [portal.msrc.microsoft.com/en-US/security-guidance/advisory/…](https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26855) - [packetstormsecurity.com/files/161846/Microsoft-Exchange-201…](http://packetstormsecurity.com/files/161846/Microsoft-Exchange-2019-SSRF-Arbitrary-File-Write.html) - [packetstormsecurity.com/files/161938/Microsoft-Exchange-Pro…](http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Execution.html) - [packetstormsecurity.com/files/162610/Microsoft-Exchange-201…](http://packetstormsecurity.com/files/162610/Microsoft-Exchange-2019-Unauthenticated-Email-Download.html) - [packetstormsecurity.com/files/162736/Microsoft-Exchange-Pro…](http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Collector.html) ## Timeline 1. ID reserved Feb 8, 2021 2. Record published Mar 2, 2021 3. Added to CISA KEV Nov 3, 2021 4. Record last updated Aug 19, 2026 ## Look up another CVE ## About CubePath CubePath is a cloud provider with data centers in Europe and the United States. It offers VPS, bare metal servers and DDoS protection. [Cloud VPS](https://cubepath.com/vps) [DDoS protection](https://cubepath.com/ddos-protection) Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 19:37 UTC. [Sources and licenses](https://cubepath.com/security/cve/legal)