Vulnerability

CVE-2026-21527

High· 6.5ZDICVSS6.5EPSS8%

.rules3/5

ZDI-26-194: Microsoft Exchange InterceptorSmtpAgent Improper Input Validation Security Feature Bypass Vulnerability

This vulnerability allows remote attackers to bypass a security feature on affected installations of Microsoft Exchange. Authentication is not required to exploit this vulnerability. The ZDI has assigned a CVSS rating of 5.3. The following CVEs are assigned: CVE-2026-21527.

Threat signal

76/100

High

Severity

high

CVSS

6.5

EPSS

Active

CVSS

v3.1via NVDOpen in FIRST calculator →

6.5/ 10MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

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 ImpactNoneNo availability impact.

EPSS

Exploit prediction · 30-day horizonFIRST.org →

8.26%

probability of exploitation in next 30 days

p95

higher than 95% of all CVEs

9-day trend↑ 0pp

Mid-pack — moderate exploitation likelihood.

Vendor VEX

No VEX statements published for CVE-2026-21527. Vendors publish VEX (Vulnerability Exploitability eXchange) to assert per-product whether a CVE is actually exploitable in their distribution.

SSVCDefer

No exploitation, limited impact or prevalence

exploitation: none
automatable: no
impact: partial
mission: support

Lifecycle

2026-03-16Published
2026-03-16Last modified2 sources

CVE-2026-21527

CVSS

EPSS

Vendor VEX

Lifecycle

References

CVE-2026-21527

CVSS

EPSS

Vendor VEX

Lifecycle

References