Microsoft Security Update Guide · Exchange
Microsoft Exchange Server Information Disclosure Vulnerability
Published
What does this mean?
- Information Disclosure. An attacker can see information that is not meant for them.
- It can be exploited over the network (including from the internet if the service is reachable there), with an ordinary user account and without any user action.
- CVSS 8.1 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 2019 Cumulative Update 14: KB5103214
15.02.1544.043 - Microsoft Exchange Server 2019 Cumulative Update 15: KB5103213
15.02.1748.048 - Microsoft Exchange Server Subscription Edition RTM: KB5103212
15.02.2562.045 - Microsoft Exchange Server 2016 Cumulative Update 23: KB5103215
15.01.2507.071
- Microsoft Exchange Server 2019 Cumulative Update 14: KB5103214
Improper authorization in Microsoft Exchange Server allows an authorized attacker to disclose information 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-285: Improper Authorization
The software does not properly check whether a user is allowed to do something.
Key facts
Released
9 jun 2026
Impact
Information Disclosure
Max severity
Important
Weakness
CVSS 3.1
8.1 / 7.1 (base / temporal)
Vector string
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N/E:U/RL:O/RC:CPublicly disclosed
No
Exploited
No
Exploitability assessment
Exploitation Unlikely
Customer action required
Yes
Links
CVSS metrics
| Base score metrics | |
|---|---|
| Attack Vector | Network |
| Attack Complexity | Low |
| Privileges Required | Low |
| User Interaction | None |
| Scope | Unchanged |
| Confidentiality | High |
| Integrity | High |
| Availability | None |
| Temporal score metrics | |
| Exploit Code Maturity | Unproven |
| Remediation Level | Official Fix |
| Report Confidence | Confirmed |
Affected products and updates
| Product | Update | Build |
|---|---|---|
| Microsoft Exchange Server 2019 Cumulative Update 14 | KB5103214 | 15.02.1544.043 |
| Microsoft Exchange Server 2019 Cumulative Update 15 | KB5103213 | 15.02.1748.048 |
| Microsoft Exchange Server Subscription Edition RTM | KB5103212 · Security Update | 15.02.2562.045 |
| Microsoft Exchange Server 2016 Cumulative Update 23 | KB5103215 | 15.01.2507.071 |
FAQ
- How could an attacker exploit this vulnerability?
- An authenticated Outlook Web App user could exploit this issue by reusing a valid access token issued to their own mailbox to access attachments stored in another user’s mailbox within the same Exchange organization, without authorization.
- What type of information could be disclosed by this vulnerability?
- An attacker could gain unauthorized access to email attachments stored in other users’ mailboxes within the same organization, which may include documents, images, or other files attached to emails.
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.
