CVE-2026-21260
Published: 10 February 2026
Summary
CVE-2026-21260 is a high-severity Exposure of Sensitive Information to an Unauthorized Actor (CWE-200) vulnerability in Microsoft Office Long Term Servicing Channel. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 15.6th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
Threat & Defense at a Glance
Threat & Defense Details
Likely Mitigating ControlsAI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Automated marking applies security attributes to system outputs, making it harder for attackers to exploit unmarked sensitive information leading to unauthorized exposure.
Proper attribute retention and permitted-value enforcement limits unauthorized actors from accessing sensitive information lacking correct labels.
Prevents unauthorized exposure of sensitive information by prohibiting untrusted external systems from processing or storing it.
By enforcing authorization matching prior to sharing, the control reduces the risk of exposing sensitive information to unauthorized actors.
Review and removal of nonpublic information from publicly accessible systems directly prevents exposure of sensitive data to unauthorized actors.
Data mining protection mechanisms detect and block unauthorized bulk extraction of sensitive data, directly mitigating exposure to unauthorized actors.
Literacy training teaches users to recognize and avoid actions that result in unauthorized exposure of sensitive information.
Retaining and monitoring training records confirms personnel have completed privacy and security awareness training on handling sensitive data, reducing the chance of unauthorized exposure due to lack of knowledge.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Remote unauthenticated info disclosure in Outlook directly enables exploitation of a public-facing client application (T1190) and facilitates spoofing via obtained sensitive data (T1557).
NVD Description
Exposure of sensitive information to an unauthorized actor in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.
Deeper analysisAI
CVE-2026-21260, published on 2026-02-10, is a vulnerability involving the exposure of sensitive information to an unauthorized actor in Microsoft Office Outlook. This issue, classified under CWE-200, enables an unauthorized attacker to perform spoofing over a network and carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N), indicating high confidentiality impact with network accessibility, low attack complexity, and no requirements for privileges or user interaction.
An unauthorized attacker can exploit this vulnerability remotely over the network without authentication or user involvement. Exploitation allows the attacker to access sensitive information and conduct spoofing attacks, potentially enabling further deception or reconnaissance activities.
Microsoft's Security Response Center provides guidance on mitigation and patching in its update guide at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21260.
Details
- CWE(s)