ProxyShell — Microsoft Exchange Server 2013 Cumulative Update 23 Vulnerability
CVE-2021-34473
Microsoft Exchange Server Remote Code Execution Vulnerability
EPSS: 0.942 (99.9th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:U/RL:O/RC:C.
Affected products
- Microsoft Exchange Server 2013 Cumulative Update 23 — versions 15.00.0
- Microsoft Exchange Server 2016 Cumulative Update 19 — versions 15.01.0
- Microsoft Exchange Server 2016 Cumulative Update 20 — versions 15.01.0
- Microsoft Exchange Server 2019 Cumulative Update 8 — versions 15.02.0
- Microsoft Exchange Server 2019 Cumulative Update 9 — versions 15.02.0
CISA KEV (Known Exploited Vulnerabilities)
This CVE is on the CISA KEV catalog, added on . 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: .
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-2021-34473 (x_refsource_MISC)
- www.zerodayinitiative.com/advisories/ZDI-21-821/ (x_refsource_MISC)
- packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-… (x_refsource_MISC)
Frequently asked questions
- What is CVE-2021-34473?
- CVE-2021-34473 is a critical-severity vulnerability in Microsoft Exchange Server 2013 Cumulative Update 23. CVSS score: 9.1/10. Published 2021-07-14.
- How severe is CVE-2021-34473?
- Critical severity. CVSS v3 base score is 9.1 out of 10.
- Is CVE-2021-34473 known to be exploited?
- Yes. CVE-2021-34473 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 116 public proof-of-concept repositories are indexed.