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CVE-2021-34523

98
FAUCET Score

CVE-2021-34523 is a critical Elevation of Privilege vulnerability affecting Microsoft Exchange Server, allowing unauthenticated attackers to gain high privileges. With a CVSS score of 9.8, it is easily exploitable over the network with no user interaction, leading to complete compromise of confidentiality, integrity, and availability. This vulnerability is actively exploited in the wild, including in ransomware campaigns, and has publicly available Metasploit modules. It has garnered significant community attention and media coverage, indicating its widespread impact and concern.

Impacted Technologies

VendorProductVersion(s)CPE
2013CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*
2016CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*
2016CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_20:*:*:*:*:*:*
2019CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*
2019CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_9:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.0CRITICAL

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

Attack Vector
LOCAL
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
NONE
Exploitability Score
2.5
Impact Score
5.8
CvssVersion
3.1

Exploit Intelligence

EPSS Score
99.99%
Probability of exploitation in next 30 days
EPSS Percentile
100.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
Added to KEV · Nov 3, 2021
Metasploit: Microsoft Exchange ProxyShell RCE · Apr 6, 2021
This CVE's current EPSS score of 0.9999 is in the 100th percentile among its peer group of 36,862 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (6)

microsoftpatch availablevia nvd_reference
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2013 Cumulative Update 23Fixed in: 15.00.1497.015
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2019 Cumulative Update 9Fixed in: 15.02.0858.010
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2016 Cumulative Update 20Fixed in: 15.01.2242.008
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2016 Cumulative Update 19Fixed in: 15.01.2176.012
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2019 Cumulative Update 8Fixed in: 15.02.0792.013
View patch

Vendor Advisories (1)

microsoft2021-Jul/CVE-2021-34523Important

Microsoft Exchange Server Elevation of Privilege Vulnerability

Jul 13, 2021

References

cisa.gov / known-exploited-vulnerabilities-catalog
US Government Resource
packetstormsecurity.com / files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html
ExploitThird Party AdvisoryVDB Entry
portal.msrc.microsoft.com / en-US/security-guidance/advisory/CVE-2021-34523
PatchVendor Advisory
zerodayinitiative.com / advisories/ZDI-21-822
Third Party AdvisoryVDB Entry