VulnerabilityAnalyzed
CVE-2026-56191
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
CRITICAL 10.0EPSS 0.90%
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.90%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
- CVSS 3.1
- 10.0 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
- EPSS
- 0.90% probability · 59th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-287
- Affected
- microsoft/exchange online
- Source
- secure@microsoft.com
EPSS 0.9% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.