CVE-2026-56191
Microsoft Exchange Online Tampering Vulnerability
CVE-2026-56191 is a critical vulnerability (CVSS 10.0) in Microsoft Exchange Online, published July 24, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.90%, the 60th percentile. No source names a fixed version.
- Severity
- 10.0 CriticalCVSS 3.1, CVE List
- Exploit chance
- 0.90%EPSS, 60th percentile
- Exploitation
- None knownNot on CISA’s or ENISA’s lists
- Fixed in
- No fix listedNo source names one
Description
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Exploit likelihood
Affected products
What each source reports
CVE List Score used
Microsoft Exchange Online Tampering Vulnerability
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
- Record
CVE-2026-56191- CVSS 3.1
- 10.0 Critical
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 - Weakness
- CWE-287
- Updated
- 2026-11-10
EUVDEUVD-2026-48458
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
- Record
EUVD-2026-48458- CVSS 3.1
- 10.0 Critical
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 - Updated
- 2026-11-11
GitHub AdvisoriesGHSA-w7qh-jvr9-qmx9
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform...
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
- Record
GHSA-w7qh-jvr9-qmx9- CVSS 3.1
- 10.0 Critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H - Weakness
- CWE-287
- Updated
- 2026-11-02
NVD
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
- Record
CVE-2026-56191- CVSS 3.1
- 10.0 Critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H - Weakness
- CWE-287
- Updated
- 2026-11-02
History
| Recorded | Changed | Sources |
|---|---|---|
| facts | CVE List | |
| first indexed | CVE List, EUVD, GitHub Advisories, NVD |
Dates are when Every CVE recorded each change. Upstream dates may differ.