CVE-2023-36757

Exploitation likely. EPSS gives it a 37% chance of exploitation in the next 30 days. A vendor fix is available.

CVSS 3.18.0High EPSS percentile98th37% chance in 30 days CISA KEVNot listedNo confirmed exploitation
No public exploit known FixVendor fixNo build named by the sources

Published 2023-09-12Updated 2024-11-21Sources: CVE.org, NVD, BDU

NVD CVE.org

What to do

The vendor has published a fix. Version details are below where the sources state them.

Steps

Written by AI from the record

Check whether your Microsoft Exchange Server is Exchange Server 2016 CU23 or Exchange Server 2019 CU12 or CU13, and record its current build number.
Update Exchange Server 2016 CU23 to build 15.01.2507.032.
Update Exchange Server 2019 CU12 to build 15.02.1118.037 or Exchange Server 2019 CU13 to build 15.02.1258.025.
Have IT confirm the update installed successfully and investigate unexpected mailbox, account, or mail-flow changes.

Vendor advisory Usually a quick update

Check it yourselfA free OpenVAS check exists for this CVE. Run it against your hosts.Is your organisation exposed?Request an assessment to establish which checks fit your systems.

What it is

From the CVE record

Microsoft Exchange Server Spoofing Vulnerability

In plain language

Written by AI from the record

Businesses using the listed Microsoft Exchange Server updates should schedule the available security update soon to prevent an attacker from impersonating trusted communications or taking control of email services.

CWE-502 deserialization weakness in Microsoft Exchange Server, reachable from an adjacent network by an attacker with low privileges, with high potential confidentiality, integrity, and availability impact.

If you're affected

Email impersonation risk
Mailbox data exposure
Email data alteration
Mail service disruption
Business communication compromise

What is it

This is a flaw in the software that runs business email. Think of it as a weakness in the mailroom’s verification process: someone with limited access nearby may be able to make harmful requests appear legitimate, potentially affecting messages and the email service itself.

Who is affected

This matters to you if you run Microsoft Exchange Server, particularly Exchange Server 2016 CU23 or Exchange Server 2019 CU12 or CU13. The attacker must already have low-level access and be able to reach the server from an adjacent network.

How urgent is it

An attacker with low-level access on an adjacent network can target affected email servers, so treat this as an urgent scheduled update. It is not listed in CISA’s catalog of vulnerabilities known to be exploited, and no public exploit code is recorded, which supports an amber rather than emergency response.

What to do — in detail

Confirm the installed Exchange cumulative update and build number, then compare it with the affected builds. For Exchange Server 2016 CU23, target 15.01.2507.032; for Exchange Server 2019 CU12, target 15.02.1118.037; and for Exchange Server 2019 CU13, target 15.02.1258.025.

Obtain the applicable vendor update through the Microsoft Security Response Center guidance, test it in the normal change process where possible, and verify the resulting build after installation. If patching must wait, limit access to the Exchange server from adjacent networks, review and restrict low-privilege accounts, and investigate unexpected mailbox, account, or mail-flow activity. No CISA KEV remediation due date applies because this CVE is not listed in KEV.

Technical context

CVSS v3.1 is 8.0 (High): AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. The reported weakness is CWE-502, with the public description identifying a Microsoft Exchange Server spoofing vulnerability; the findings do not provide a more specific vulnerable component or request format. No CISA KEV listing and no public exploit code are recorded. EPSS predicts a 36.9% likelihood (98th percentile), with a rising trend; this is predictive rather than confirmation of exploitation.

This is a general assessment based on public vulnerability data. It does not account for your specific infrastructure — when in doubt, consult a security specialist.

Exploitation

Where each signal puts this CVE on the scale from published to confirmed exploited.

EPSS98th

CISA KEV

Not in the catalog. CISA has not confirmed exploitation.

Public exploits

No public exploit or proof of concept found in the sources we track.

EPSS

37% chance of exploitation activity in the next 30 days, which ranks it in the 98th percentile of scored CVEs.

Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.

Lifecycle

9 events over 1097 days, from the signal feeds we watch.

2026-09-13EPSS band changehigh → moderateepss band change
2026-06-25OpenVAS check added
2026-06-22EPSS band changelow → high
2024-11-21Patch availablerecord updated
2023-09-12Publishedweakness classified, att&ck mapped

Affected products

Microsoft Corpcommercial · USaka microsoft, microsoft corporation

Technical detail

CVSS 3.1 vector

Open in the CVSS calculator

CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Scored 8.0 by NVD.

How it is reached

Attack Vector AdjacentRequires access to the local network (e.g. same Wi-Fi, Bluetooth)
Attack Complexity LowNo special conditions — the attack can be reliably reproduced
Privileges Required LowRequires basic user-level privileges
User Interaction NoneNo user interaction needed — fully automated exploitation

Scope

Scope UnchangedImpact is limited to the vulnerable component itself

Impact if exploited

Confidentiality HighTotal information disclosure — all data in the component is compromised
Integrity HighTotal loss of integrity — attacker can modify any data in the component
Availability HighTotal denial of service — the component is completely unavailable

Weaknesses

ATT&CK techniques

Mapped from the weaknesses above (CWE to ATT&CK), not observed in attacks.

Sources

References in the record

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