Vulnerability

CVE-2021-33766

High· 7.3KEVCVSS7.3EPSS94%

.rules3/5

Microsoft Exchange Server Information Disclosure

Microsoft Exchange Server contains an information disclosure vulnerability which can allow an unauthenticated attacker to steal email traffic from target.

Threat signal

99/100

Severe

Severity

high

CVSS

7.3

EPSS

94%

Active

KEV

CISA KEV — actively exploited

1595d overdue

AffectedMicrosoft — Exchange Server

Added to KEV

2022-01-18

Federal patch due (BOD 22-01)

2022-02-01

Required action (CISA verbatim)

Apply updates per vendor instructions.

Vendor advisory + references

https://nvd.nist.gov/vuln/detail/CVE-2021-33766

CISA description: “Microsoft Exchange Server contains an information disclosure vulnerability which can allow an unauthenticated attacker to steal email traffic from target.”

CVSS

v3.1Open in FIRST calculator →

7.3/ 10HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

Attack VectorNetworkExploitable remotely over the internet — no local access needed.
Attack ComplexityLowNo special conditions — exploit works reliably.
Privileges RequiredNoneUnauthenticated — no credentials needed.
User InteractionNoneFully automated — no victim action needed.
ScopeUnchangedImpact contained to the vulnerable component.
Confidentiality ImpactLowSome data disclosure; attacker doesn't fully control what.
Integrity ImpactLowSome data modification; attacker doesn't fully control extent.
Availability ImpactLowReduced performance / interruptions.

EPSS

Exploit prediction · 30-day horizonFIRST.org →

93.8%

probability of exploitation in next 30 days

p100

higher than 100% of all CVEs

5-day trend↑ 0pp

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

Vendor VEX

No VEX statements published for CVE-2021-33766. 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: no
impact: total
mission: support

Lifecycle

2022-01-18Added to CISA KEVransomware: Unknown
2022-01-18Published
2022-02-01Federal 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.