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CVE-2025-64666VulnerabilityPublished Updated

CVE-2025-64666: Microsoft Exchange Server 2016 Cumulative Update 23 · Improper Input Validation

Affects Microsoft Exchange Server 2016 Cumulative Update 23Source CVE Database V5

0

Not known to be exploited · CVSS 7.5 High · patch available : patch Microsoft Exchange Server 2016 Cumulative Update 23 soon.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 3.1 base score
7.5High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
1.0% chance of exploitation in 30 days – higher than 63% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 9 Dec 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-26.

What to do

Affected software

ProductAffectedFixed in
Microsoft Microsoft Exchange Server 2016 Cumulative Update 23Affected
  • =15.01.0.0
Fixed in–

AI-suggested

A patch is available for this vulnerability. It is recommended to apply the official Microsoft update for Exchange Server 2016 Cumulative Update 23 to remediate this issue. Since this is not a cloud service, administrators must manually deploy the patch. No additional vendor advisory content contradicts this guidance.

Description

Improper input validation in Microsoft Exchange Server allows an authorized attacker to elevate privileges over a network.

References

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