Vulnerability · Published Jul 24, 2026 · Assigned by microsoft
CVE-2026-56191Microsoft Exchange Online Tampering Vulnerability
Critical 10.0
In plain English
A critical-severity improper authentication in Microsoft Exchange Online from Microsoft. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.9% (higher than 60% of all known vulnerabilities).
Severity (CVSS 3.1)10.0Critical
Exploit odds (30 days)0.9%top 40.1% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Microsoft | Microsoft Exchange Online | - |
Weakness: CWE-287 · 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
References
- Microsoft Exchange Online Tampering Vulnerability vendor-advisory, patch