Vulnerability

CVE-2021-34523

Critical· 9.0KEVEXPLOITCVSS9EPSS94%

.rules3/5

Microsoft Exchange Server Privilege Escalation Vulnerability

Microsoft Exchange Server contains an unspecified vulnerability that allows for privilege escalation.

Threat signal

100/100

Severe

Severity

critical

CVSS

9.0

EPSS

94%

Active

KEV

CISA KEV — actively exploited

Ransomware: Known1669d overdue

AffectedMicrosoft — Exchange Server

Added to KEV

2021-11-03

Federal patch due (BOD 22-01)

2021-11-17

Required action (CISA verbatim)

Apply updates per vendor instructions.

Vendor advisory + references

https://nvd.nist.gov/vuln/detail/CVE-2021-34523

CISA description: “Microsoft Exchange Server contains an unspecified vulnerability that allows for privilege escalation.”

CVSS

v3.1Open in FIRST calculator →

9.0/ 10CRITICALCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

Attack VectorLocalRequires local access — shell, console, or local app.
Attack ComplexityLowNo special conditions — exploit works reliably.
Privileges RequiredNoneUnauthenticated — no credentials needed.
User InteractionNoneFully automated — no victim action needed.
ScopeChangedImpact extends beyond the vulnerable component (e.g. sandbox escape).
Confidentiality ImpactHighTotal disclosure of sensitive data.
Integrity ImpactHighTotal compromise of integrity — full data modification possible.
Availability ImpactNoneNo availability impact.

EPSS

Exploit prediction · 30-day horizonFIRST.org →

94.0%

probability of exploitation in next 30 days

p100

higher than 100% of all CVEs

3-day trend↑ 0pp

Statistically about to be weaponized — top-tier triage urgency.

Vendor VEX

No VEX statements published for CVE-2021-34523. Vendors publish VEX (Vulnerability Exploitability eXchange) to assert per-product whether a CVE is actually exploitable in their distribution.

SSVCAct

Active exploitation with total impact on essential/support systems

exploitation: active
automatable: yes
impact: total
mission: support

Lifecycle

2021-11-03Added to CISA KEVransomware: Known
2021-11-03Public exploit observedmetasploit
2021-11-03Published
2021-11-17Federal patch due (BOD 22-01)
2026-06-12Last modified1 source

No source-event history recorded yet. New revisions will appear here as ingestors re-fetch this CVE.