CVE-2026-56191: Microsoft Exchange Online Tampering Vulnerability
Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.
CSIRTS triage
- What
- Improper authentication allows an unauthorized attacker to perform tampering over a network.
- Who is affected
- Deployments of Microsoft Exchange Online.
- Urgency
- Remediation is urgent due to the critical severity and potential for exploitation.
- Action
- Apply the latest security updates from Microsoft.
AI-assisted analysis generated from the source advisory — verify against the original.
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Details
Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56191
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Low exploitation riskCVE-2026-561910.67% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 48% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2026-56191 | coverage & exploitation status | NVD · CVE.org |
Same CVEs, other sources
How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.
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