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 if a user takes part, for example by opening a link or file.
- CVSS 7.5 out of 10: high. Microsoft rates it Important.
- No attacks reported; Microsoft expects exploitation to be less 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: KB5103212
15.02.2562.045 - Microsoft Exchange Server 2019 Cumulative Update 15: KB5103213
15.02.1748.048 - Microsoft Exchange Server 2019 Cumulative Update 14: KB5103214
15.02.1544.043 - Microsoft Exchange Server 2016 Cumulative Update 23: KB5103215
15.01.2507.071
- Microsoft Exchange Server Subscription Edition RTM: KB5103212
Improper control of generation of code ('code injection') 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.
What kind of flaw is this?
- CWE-94: Improper Control of Generation of Code ('Code Injection')
An attacker can supply code that the software then runs (code injection).
Key facts
Released
9 jun 2026
Impact
Remote Code Execution
Max severity
Important
Weakness
CVSS 3.1
7.5 / 6.5 (base / temporal)
Vector string
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:CPublicly disclosed
No
Exploited
No
Exploitability assessment
Exploitation Less Likely
Customer action required
Yes
Links
CVSS metrics
| Base score metrics | |
|---|---|
| Attack Vector | Network |
| Attack Complexity | High |
| Privileges Required | None |
| User Interaction | Required |
| 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 | KB5103212 · Security Update | 15.02.2562.045 |
| Microsoft Exchange Server 2019 Cumulative Update 15 | KB5103213 | 15.02.1748.048 |
| Microsoft Exchange Server 2019 Cumulative Update 14 | KB5103214 | 15.02.1544.043 |
| Microsoft Exchange Server 2016 Cumulative Update 23 | KB5103215 | 15.01.2507.071 |
FAQ
- According to the CVSS metric, the attack complexity is high (AC:H). What does this mean for this vulnerability?
- Exploitation depends on an attacker being able to place themselves in a machine‑in‑the‑middle position on the network during use of the affected script. Because this requires specific network conditions that are not commonly present, the vulnerability is more difficult to exploit than issues that can be triggered directly.
- How could an attacker exploit this vulnerability?
- An attacker who is able to intercept network traffic could interfere with the secure connection used by the Exchange migration script and inject malicious data. When the script is run during a hybrid migration, this could cause unintended commands to run on the on‑premises Exchange server with administrative permissions.
- Is there anything to be done in addition to installing the June 2026 security updates for my Exchange Server?
- Yes, Microsoft recommends that customers download and use the latest, fixed version of the Public Folder scripts. The versions of the Public Folder scripts included with Exchange Server are outdated and will be removed in a future update. Customers can download the latest version of the Public Folder scripts here.
Revisions
| Version | Date | Note |
|---|---|---|
| 1 | 9 jun 2026 | Information published. |
What changed in Microsoft 365 this week? →
View at Microsoft → ← All security advisories
Source: Microsoft Security Update Guide. 365Fanatic is not affiliated with Microsoft.
