Microsoft Security Update Guide · Exchange
Microsoft Exchange Server Remote Code Execution Vulnerability
Published
What does this mean?
- Remote Code Execution. An attacker can run their own code on the system remotely. This is the most serious type: it can lead to taking over the system.
- It can be exploited over the network (including from the internet if the service is reachable there), without an account and without any user action.
- CVSS 8.1 out of 10: high. Microsoft rates it Critical.
- No attacks reported yet, but Microsoft expects exploitation to be likely.
- What should you do? Install the security update for the version you run (or a later cumulative update):
- Microsoft Exchange Server Subscription Edition RTM: KB5128895
15.02.2562.056 - Microsoft Exchange Server 2019 Cumulative Update 15: KB5128896
15.02.1748.055 - Microsoft Exchange Server 2019 Cumulative Update 14: KB5128897
15.02.1544.050 - Microsoft Exchange Server 2016 Cumulative Update 23: KB5128898
15.01.2507.077
- Microsoft Exchange Server Subscription Edition RTM: KB5128895
Stack-based buffer overflow in Microsoft Exchange Server allows an unauthorized attacker to execute code over a network.
How do I check if I am affected?
Exchange Server: check and update
- Check your server versions in the Exchange Management Shell:
Get-ExchangeServer | Format-List Name,AdminDisplayVersion - Microsoft's Exchange Health Checker (CSS-Exchange on GitHub) shows which updates are missing per server.
- Install the security update (SU) for the CU you run. Microsoft updates Exchange Online.
Key facts
Released
13 okt 2026
Impact
Remote Code Execution
Max severity
Critical
Weakness
CVSS 3.1
8.1 / 7.1 (base / temporal)
Vector string
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:CPublicly disclosed
No
Exploited
No
Exploitability assessment
Exploitation More Likely
Customer action required
Yes
Links
CVSS metrics
| Base score metrics | |
|---|---|
| Attack Vector | Network |
| Attack Complexity | High |
| Privileges Required | None |
| User Interaction | None |
| Scope | Unchanged |
| Confidentiality | High |
| Integrity | High |
| Availability | High |
| Temporal score metrics | |
| Exploit Code Maturity | Unproven |
| Remediation Level | Official Fix |
| Report Confidence | Confirmed |
Affected products and updates
| Product | Update | Build |
|---|---|---|
| Microsoft Exchange Server Subscription Edition RTM | KB5128895 · Security Update | 15.02.2562.056 |
| Microsoft Exchange Server 2019 Cumulative Update 15 | KB5128896 | 15.02.1748.055 |
| Microsoft Exchange Server 2019 Cumulative Update 14 | KB5128897 | 15.02.1544.050 |
| Microsoft Exchange Server 2016 Cumulative Update 23 | KB5128898 | 15.01.2507.077 |
FAQ
- How could an attacker exploit this vulnerability?
- An unauthenticated attacker could send a specially crafted email to an affected Exchange server, triggering an internal content-conversion process. Successful exploitation could allow the attacker to execute code on the server. Exploitation requires an attacker to have a deep understanding of the target environment and is not guaranteed to succeed. User interaction is not required.
- According to the CVSS metric, the attack complexity is high (AC:H). What does that mean for this vulnerability?
- Successful exploitation of this vulnerability requires an attacker to have a deep understanding of the system. Successful exploitation is not guaranteed and depends on a combination of factors that might include the environment, system configuration, and the presence of additional security measures.
Revisions
| Version | Date | Note |
|---|---|---|
| 1 | 13 okt 2026 | Information published. |
This is in the weekly digest for week 42: everything that changed in Microsoft 365 this week. →
View at Microsoft → ← All security advisories
Source: Microsoft Security Update Guide. 365Fanatic is not affiliated with Microsoft.
