Microsoft 365 Apps for Enterprise: Exposure of Sensitive Information to an Unauthorized Actor
CVE-2026-21260 is a high-severity exposure of sensitive information to an unauthorized actor vulnerability in Microsoft 365 Apps for Enterprise from Microsoft, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version https://aka.ms/OfficeSecurityReleases as the first without the flaw, so updating Microsoft 365 Apps for Enterprise to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 1.5% chance of exploitation within 30 days, higher than 75% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Microsoft 365 Apps for Enterprise to https://aka.ms/OfficeSecurityReleases or a later version.
- Update Microsoft Office 2019 to https://aka.ms/OfficeSecurityReleases or a later version.
- Update Microsoft Office LTSC 2021 to https://aka.ms/OfficeSecurityReleases or a later version.
- Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Microsoft 365 Apps for Enterprise | 16.0.1 up to, but not including, https://aka.ms/OfficeSecurityReleases | https://aka.ms/OfficeSecurityReleases |
| Microsoft | Microsoft Office 2019 | 19.0.0 up to, but not including, https://aka.ms/OfficeSecurityReleases | https://aka.ms/OfficeSecurityReleases |
| Microsoft | Microsoft Office LTSC 2021 | 16.0.1 up to, but not including, https://aka.ms/OfficeSecurityReleases | https://aka.ms/OfficeSecurityReleases |
| Microsoft | Microsoft Office LTSC 2024 | 16.0.0 up to, but not including, https://aka.ms/OfficeSecurityReleases | https://aka.ms/OfficeSecurityReleases |
| Microsoft | Microsoft Outlook 2016 | 16.0.0.0 up to, but not including, 16.0.5539.1002 | 16.0.5539.1002 |
| Microsoft | Microsoft SharePoint Enterprise Server 2016 | 16.0.0 up to, but not including, 16.0.5539.1002 | 16.0.5539.1002 |
| Microsoft | Microsoft SharePoint Server 2019 | 16.0.0 up to, but not including, 16.0.10417.20097 | 16.0.10417.20097 |
| Microsoft | Microsoft SharePoint Server Subscription Edition | 16.0.0 up to, but not including, 16.0.19127.20518 | 16.0.19127.20518 |
| Microsoft | 365 Apps | Not specified in the record | Not stated |
| Microsoft | Office | 2019 | Not stated |
| Microsoft | Office Long Term Servicing Channel | 2021; 2024 | Not stated |
| Microsoft | Outlook | 2016 | Not stated |
| Microsoft | Sharepoint Server | before 16.0.19127.20518; 2016; 2019 | 16.0.19127.20518 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- NoneNothing can be modified.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. Scored by CNA (microsoft.com).
Official description
Exposure of sensitive information to an unauthorized actor in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Exposure of Sensitive Information to an Unauthorized Actor
The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
How developers prevent this class of flaw
- Compartmentalize the system to have safe areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
More Exposure of Sensitive Information to an Unauthorized Actor vulnerabilities (CWE-200)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Other vulnerabilities in Microsoft 365 Apps for Enterprise
- 8.8 High severity
- 6.5 Medium severity
Recent Exposure of Sensitive Information to an Unauthorized Actor vulnerabilities
- 5.9 Medium severity
- 7.5 High severity
- 7.5 High severity
- 9.1 Critical severity
- 7.5 High severity
- 7.6 High severity
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