How severe is CVE-2021-26857?

High severity. CVSS v3 base score is 7.8 out of 10.

Is CVE-2021-26857 known to be exploited?

Yes. CVE-2021-26857 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 64 public proof-of-concept repositories are indexed.

Vulnerability in Microsoft Exchange Server 2010 Service Pack 3

CVE-2021-26857

Microsoft Exchange Server Remote Code Execution Vulnerability

EPSS: 0.394 (97.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.8 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C.

Affected products

Microsoft Exchange Server 2010 Service Pack 3 — versions 14.0.0.0
Microsoft Exchange Server 2013 Cumulative Update 21 — versions 15.00.0
Microsoft Exchange Server 2013 Cumulative Update 22 — versions 15.00.0
Microsoft Exchange Server 2013 Cumulative Update 23 — versions 15.00.0
Microsoft Exchange Server 2013 Service Pack 1 — versions 15.00.0
Microsoft Exchange Server 2016 Cumulative Update 10 — versions 15.01.0
Microsoft Exchange Server 2016 Cumulative Update 11 — versions 15.01.0
Microsoft Exchange Server 2016 Cumulative Update 12 — versions 15.01.0
Microsoft Exchange Server 2016 Cumulative Update 13 — versions 15.01.0
Microsoft Exchange Server 2016 Cumulative Update 14 — versions 15.01.0

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2021-11-03. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2022-05-03.

Required action: Apply updates per vendor instructions.

Known ransomware campaign use: yes.

Public proof-of-concept exploits

References

portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26857 (x_refsource_MISC)

Frequently asked questions

What is CVE-2021-26857?: CVE-2021-26857 is a high-severity vulnerability in Microsoft Exchange Server 2010 Service Pack 3. CVSS score: 7.8/10. Published 2021-03-02.
How severe is CVE-2021-26857?: High severity. CVSS v3 base score is 7.8 out of 10.
Is CVE-2021-26857 known to be exploited?: Yes. CVE-2021-26857 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 64 public proof-of-concept repositories are indexed.