CVE-2023-36756

Exploitation likely. EPSS gives it a 49% chance of exploitation in the next 30 days. A vendor fix is available.

CVSS 3.18.0High EPSS percentile99th49% 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 2016 CU23, 2019 CU12, or 2019 CU13, and note its installed build number.
Update Exchange Server 2016 CU23 to 15.01.2507.032, Exchange Server 2019 CU13 to 15.02.1258.025, or Exchange Server 2019 CU12 to 15.02.1118.037.
Confirm the installed build after updating and investigate unexpected use of Exchange accounts.

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 Remote Code Execution Vulnerability

In plain language

Written by AI from the record

This affects unpatched Microsoft Exchange Server 2016 CU23 and 2019 CU12 or CU13, and a typical small business using them should schedule the available update promptly.

Authenticated, adjacent-network remote code execution in Microsoft Exchange Server through unsafe deserialization (CWE-502), affecting the listed unpatched cumulative-update builds.

If you're affected

Email system takeover
Mailbox data exposure
Business email disruption
Network compromise

What is it

This is a flaw in an email server that can let an improperly authorized person run their own instructions on it. Think of it as someone with a staff key finding a way to reach the building’s control room, rather than being limited to the rooms their key should open.

Who is affected

This matters if you run Microsoft Exchange Server for company email. It is only a risk if an attacker has a valid login and can reach the server from a nearby network.

How urgent is it

An attacker who has a valid login and nearby network access can use this flaw to take control of the affected email server, making this an amber-priority update. There is no confirmed public exploitation, no public exploit code on record, and it is not listed in CISA’s known-exploited catalog.

What to do — in detail

Confirm the Exchange cumulative update and installed build on each server. Apply the Microsoft security update that brings Exchange Server 2016 CU23 to 15.01.2507.032, Exchange Server 2019 CU13 to 15.02.1258.025, or Exchange Server 2019 CU12 to 15.02.1118.037; use the vendor guidance at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-36756. No CISA KEV remediation due date applies because this CVE is not in KEV. If patching is delayed, restrict Exchange access to trusted network segments and review accounts that can authenticate to the server; monitor for unexpected account use and unusual server activity after remediation.

Technical context

CVE-2023-36756 is CVSS 8.0 High (CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H). The reported weakness is CWE-502, unsafe deserialization, with an adjacent-network attack vector, low complexity, required privileges, and no user interaction. It is not listed in CISA KEV and no public exploit code is on record. EPSS predicts a 49.2% likelihood (99th percentile) and is rising; this is a prediction, not evidence of confirmed 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.

EPSS99th

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

49% chance of exploitation activity in the next 30 days, which ranks it in the 99th percentile of scored CVEs.

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

Lifecycle

9 events over 1098 days, from the signal feeds we watch.

2026-09-14EPSS 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

msrc.microsoft.com/update-guide/vulnerability/CVE-2023-36756

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