Microsoft Exchange Online Tampering Vulnerability
CVE-2026-56191 is a tampering vulnerability in Microsoft Exchange Online (rated Critical, CVSS 10.0). Microsoft fixed it in the service; customers need to do nothing.
1 version
Facts
- Microsoft id
CVE-2026-56191- Products
- Microsoft Exchange Online
- Severity
- Critical
- Impact
- Tampering
- CVSS
- 10.0
- CVSS vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C
- Exploited
- No
- Publicly disclosed
- No
- Customer action required
- No
- Release
- 2026-Jul
- Assigned by
- Microsoft
- Weakness
- CWE-287: Improper Authentication
- MSRC revision
- 1.0
- Status pages
- Exchange Online status
- First captured by us
- (from our first import of this list)
- Microsoft last modified
- Source
- Security updates · open the original at Microsoft
Microsoft's revision notes
- Revision 1.0, 2026-07-23:
Information published.
Microsoft says
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
What Microsoft changed
One version so far. If Microsoft edits it, each change shows here with what was removed and added.
First version we captured ·
The text as we first saw it
Seen by us · Microsoft's timestamp · Microsoft's page
Related changes
Other changes for Exchange Online
- Where is Exchange SE CU1 anyway?
- Understanding the new 100 GB mailbox entitlement for Microsoft 365 Business suites
- Notes from the field: testing EWSAllowedAppIDs safely
- Help us shape Exchange Server on-premises to different online org Free/Busy after EWS retirement
- Tell us how you use ObjectGuid, SamAccountName, and DistinguishedName in Exchange Online
- Exchange 2016/2019: Throttling and Blocking up to the Final Public Update Baseline
- Take control of your EWSAllowedAppIDs list before EWS access changes
- Exchange Server AD FS Modern Authentication: Expanded Outlook client support
Last updated