CVE-2026-56191
CriticalCVSS 10.0Exploitation Probability (EPSS)
Low risk49th percentile - higher than 49% of all known CVEs
Summary
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
Risk Assessment
An unauthorized attacker can modify data in Exchange Online, potentially leading to integrity breaches of email and other data.
Recommendation
Apply the security update provided by Microsoft for Microsoft Exchange Online.
Other vulnerabilities in Microsoft Exchange Online
See all- CVE-2026-65801Critical
Server-side request forgery (SSRF) in Microsoft Exchange Online allows an unauthorized attacker to elevate privileges over a network.
- CVE-2026-48582Critical
Missing authorization in Microsoft Exchange Online allows an authorized attacker to elevate privileges over a network.
- CVE-2026-48579Critical
Improper authorization in Microsoft Exchange Online allows an unauthorized attacker to disclose information over a network.
- CVE-2026-54998High
A vulnerability in Microsoft Exchange Online allows an authorized attacker to elevate privileges over a network due to incorrect authorization.
Original NVD description (English source)
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.