Quick answers
- Is CVE-2026-56191 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-56191 being exploited in the wild.
- How severe is CVE-2026-56191?
- Critical severity, with a CVSS score of 10, published 24 July 2026.
- Which products and versions are affected?
- Microsoft Exchange Online All versions.
- Is there a fix for CVE-2026-56191?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-56191 attacked?
- It is attacked over the network, in a hosted service.
- Am I affected by CVE-2026-56191?
- Check whether you run Microsoft Exchange Online at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
A critical vulnerability (CWE-287) exists in Microsoft Exchange Online due to improper authentication mechanisms. An unauthenticated attacker can exploit this flaw over the network with low complexity and no user interaction required. Successful exploitation allows for unauthorized tampering, potentially leading to full compromise of confidentiality, integrity, and availability (CVSS 10.0). As this is an exclusively hosted service, Microsoft typically manages the deployment of fixes directly within the Exchange Online environment.
Affected products
- Microsoft Exchange Online All versions
Timeline
- 2026-07-24: advisory: NVD publication date