Microsoft Security Update Guide · Exchange
Microsoft Exchange Server Elevation of Privilege Vulnerability
Published
What does this mean?
- Elevation of Privilege. An attacker can gain more rights than they should have, for example admin rights.
- It can be exploited over the network (including from the internet if the service is reachable there), with an ordinary user account and if a user takes part, for example by opening a link or file.
- CVSS 8.0 out of 10: high. Microsoft rates it Critical.
- 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: KB5121575
15.02.1544.044 - Microsoft Exchange Server 2019 Cumulative Update 15: KB5121574
15.02.1748.049 - Microsoft Exchange Server Subscription Edition RTM: KB5121573
15.02.2562.046 - Microsoft Exchange Server 2016 Cumulative Update 23: KB5121576
15.01.2507.072
- Microsoft Exchange Server 2019 Cumulative Update 14: KB5121575
Authentication bypass by capture-replay in Microsoft Exchange Server allows an authorized attacker to elevate privileges 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
11 aug 2026
Impact
Elevation of Privilege
Max severity
Critical
Weakness
CVSS 3.1
8.0 / 7.0 (base / temporal)
Vector string
CVSS:3.1/AV:N/AC:L/PR:L/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 | Low |
| Privileges Required | Low |
| 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 2019 Cumulative Update 14 | KB5121575 | 15.02.1544.044 |
| Microsoft Exchange Server 2019 Cumulative Update 15 | KB5121574 | 15.02.1748.049 |
| Microsoft Exchange Server Subscription Edition RTM | KB5121573 · Security Update | 15.02.2562.046 |
| Microsoft Exchange Server 2016 Cumulative Update 23 | KB5121576 | 15.01.2507.072 |
FAQ
- What privileges could be gained by an attacker who successfully exploited the vulnerability?
- The attacker would be able to take over the mailboxes of all Exchange users, attackers can send emails, read emails, download attachments.
Revisions
| Version | Date | Note |
|---|---|---|
| 1 | 11 aug 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.
