CVE-2026-21535
Published: 19 February 2026
Summary
CVE-2026-21535 is a high-severity Improper Access Control (CWE-284) vulnerability in Microsoft Teams. Its CVSS base score is 8.2 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 43.7th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 AC-3 (Access Enforcement) and AU-13 (Monitoring for Information Disclosure).
Deeper analysis
CVE-2026-21535 is an improper access control vulnerability in Microsoft Teams that enables an unauthorized attacker to disclose information over a network. Published on 2026-02-19, it carries a CVSS v3.1 base score of 8.2 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N) and maps to CWE-284.
The vulnerability can be exploited by any unauthorized attacker with network access, requiring low complexity, no privileges, and no user interaction. Successful exploitation results in high-impact confidentiality loss through information disclosure, alongside low-impact integrity modification, but no availability disruption.
Mitigation guidance is available in the Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21535.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-7572
Vulnerability details
Improper access control in Microsoft Teams allows an unauthorized attacker to disclose information over a network.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Direct remote exploitation of public-facing Microsoft Teams application via improper access control for unauthorized information disclosure.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
AC-3 requires enforcement of approved authorizations for logical access, directly mitigating the improper access control in Microsoft Teams that enables unauthorized network-based information disclosure.
SI-2 mandates timely identification, reporting, and correction of system flaws, addressing the root cause of this CVE through patching as guided by the MSRC advisory.
AU-13 requires monitoring information systems for unauthorized disclosure, enabling detection of exploitation attempts resulting in high-impact confidentiality loss over the network.