Microsoft Security Update Guide · Exchange
Microsoft Exchange Online Tampering Vulnerability
Published
What does this mean?
- Tampering. An attacker can change data or settings without permission.
- 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 10.0 out of 10: critical. Microsoft rates it Critical.
- What should you do? Nothing: Microsoft fixed this in the cloud service. There is no update to install.
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
What kind of flaw is this?
- CWE-287: Improper Authentication
The software does not properly check who a user is (authentication).
Key facts
Released
23 jul 2026
Impact
Tampering
Max severity
Critical
Weakness
CVSS 3.1
10.0 / 8.7 (base / temporal)
Vector string
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:CPublicly disclosed
No
Exploited
No
Exploitability assessment
N/A
Customer action required
No, fixed by Microsoft
Links
CVSS metrics
| Base score metrics | |
|---|---|
| Attack Vector | Network |
| Attack Complexity | Low |
| Privileges Required | None |
| User Interaction | None |
| Scope | Changed |
| 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 Online | — | — |
FAQ
- Why are there no links to an update or instructions with steps that must be taken to protect from this vulnerability?
- This vulnerability has already been fully mitigated by Microsoft. There is no action for users of this service to take. The purpose of this CVE is to provide further transparency. Please see Toward greater transparency: Unveiling Cloud Service CVEs for more information.
Revisions
| Version | Date | Note |
|---|---|---|
| 1 | 23 jul 2026 | Information published. |
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View at Microsoft → ← All security advisories
Source: Microsoft Security Update Guide. 365Fanatic is not affiliated with Microsoft.
