How severe is CVE-2021-42305?

CVE-2021-42305 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2021-42305 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 8% (94th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-42305?

CVE-2021-42305 primarily affects Microsoft Exchange Server. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-42305?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-42305 published?

CVE-2021-42305 was published on 2021-11-10 and last updated on 2026-06-17.

CVE-2021-42305

CVE-2021-42305 is a medium-severity vulnerability in Microsoft Exchange Server with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
CVSS v2: 4.3
EPSS exploit prediction: 8% (94th percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Microsoft Exchange Server
Published: 2021-11-10
Last modified: 2026-06-17

Description

Microsoft Exchange Server Spoofing Vulnerability

Frequently asked questions

What is CVE-2021-42305?: Microsoft Exchange Server Spoofing Vulnerability
How severe is CVE-2021-42305?: CVE-2021-42305 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2021-42305 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 8% (94th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-42305?: CVE-2021-42305 primarily affects Microsoft Exchange Server. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-42305?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-42305 published?: CVE-2021-42305 was published on 2021-11-10 and last updated on 2026-06-17.

References

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42305

Affected products (5)

cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_21:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_22:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_10:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_11:*:*:*:*:*:*

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