CVE-2026-56191 Microsoft Exchange Online Tampering Vulnerability
An unauthorized attacker can bypass authentication to tamper with data in Microsoft Exchange Online via network access.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-56191?
CVE-2026-56191 is a critical authentication bypass vulnerability in Microsoft Exchange Online, published on 24 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
Weakness: CWE-287
Which versions are affected by CVE-2026-56191?
It affects 1 product.
Products include Microsoft Exchange Online.
How do I fix CVE-2026-56191?
No fix has been published for CVE-2026-56191 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-56191 being exploited?
There is no known exploitation of CVE-2026-56191 in the wild and no public exploit code.
Other vulnerabilities in Microsoft Exchange Online
- CVE-2026-65801 Microsoft Exchange Online Elevation of Privilege Vulnerability
- CVE-2026-48582 Microsoft Exchange Online Elevation of Privilege Vulnerability
- CVE-2026-48579 Microsoft Exchange Online Information Disclosure Vulnerability
- CVE-2026-54998 Microsoft Exchange Online Elevation of Privilege Vulnerability
Sources
Also known as GHSA-w7qh-jvr9-qmx9.