CVE Record
[ CRITICAL ]CVE-2021-34523
Microsoft Exchange Server Privilege Escalation Vulnerability
Microsoft Exchange Server contains an unspecified vulnerability that allows for privilege escalation.
- Vendor
- Microsoft
- Product
- Exchange Server
- CVSS
- 9.0
- EPSS (exploit probability)
- 100.0%
- Status
- kevransomware use
- CISA patch-by (BOD 22-01)
- Added to KEV
Is CVE-2021-34523 being exploited?
Yes. CISA added CVE-2021-34523 to its Known Exploited Vulnerabilities catalog on . CISA only lists a CVE when it has reliable evidence of exploitation in the wild. CISA marks it as known to be used in ransomware campaigns.
FIRST's EPSS model puts the probability of exploitation activity in the next 30 days at 100.0% (scored October 14, 2026).
- CISA KEV[ LISTED ]
- ENISA EUVD (exploited)[ — ]
- CIRCL KEV[ — ]
Catalog snapshot 2026-10-19. Full cross-catalog view: /kev-comparison
What to do
CISA required actionApply updates per vendor instructions.
US federal civilian agencies must remediate by (14 days after listing) under BOD 22-01. Everyone else: that deadline is a sensible upper bound, not a target. Vendor guidance and the NVD record are linked under Source above.
Other Microsoft Exchange Server CVEs we track
| CVE / Vulnerability | Severity | CVSS | EPSS | Added to KEV |
|---|---|---|---|---|
| CVE-2026-96940 Microsoft Exchange Server privilege escalation via weak authorizationwrite-up | [ HIGH ] | 8.8 | 0.5% | — |
| CVE-2023-21529 Microsoft Exchange Server Deserialization of Untrusted Data Vulnerabilityransomware use | [ HIGH ] | 8.8 | 59.3% | |
| CVE-2021-31196 Microsoft Exchange Server Information Disclosure Vulnerability | [ HIGH ] | 7.2 | 54.1% | |
| CVE-2024-21410 Microsoft Exchange Server Privilege Escalation Vulnerability | [ CRITICAL ] | 9.8 | 12.6% | |
| CVE-2022-41080 Microsoft Exchange Server Privilege Escalation Vulnerabilityransomware use | [ HIGH ] | 8.8 | 77.3% | |
| CVE-2022-41082 Microsoft Exchange Server Remote Code Execution Vulnerabilityransomware use | [ HIGH ] | 8.0 | 100.0% | |
| CVE-2022-41040 Microsoft Exchange Server Server-Side Request Forgery Vulnerabilityransomware use | [ HIGH ] | 8.8 | 100.0% | |
| CVE-2018-8581 Microsoft Exchange Server Privilege Escalation Vulnerabilityransomware use | [ HIGH ] | 7.4 | 27.4% |