CVE-2026-21264
Published: 22 January 2026
Summary
CVE-2026-21264 is a critical-severity Cross-site Scripting (CWE-79) vulnerability in Microsoft Account. Its CVSS base score is 9.3 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 16.1th 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 SI-10 (Information Input Validation) and SI-15 (Information Output Filtering).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
SI-10 requires validating all information inputs, directly preventing the improper neutralization of input that enables this XSS vulnerability.
SI-15 mandates filtering of information outputs during web page generation, blocking execution of injected malicious scripts.
SI-2 ensures timely identification, reporting, and patching of the specific XSS flaw in Microsoft Account, eliminating the vulnerability.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
XSS in public-facing Microsoft Account service directly enables web app exploitation (T1190) via malicious links and facilitates web session cookie theft for impersonation/data access (T1539).
NVD Description
Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Account allows an unauthorized attacker to perform spoofing over a network.
Deeper analysisAI
CVE-2026-21264 is a cross-site scripting (XSS) vulnerability stemming from improper neutralization of input during web page generation, classified under CWE-79. It affects the Microsoft Account service and was published on January 22, 2026, with a CVSS v3.1 base score of 9.3 (AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N), marking it as critical due to its high potential impact.
The vulnerability can be exploited by an unauthorized attacker over a network, requiring low attack complexity, no privileges, and user interaction such as clicking a malicious link. Successful exploitation enables spoofing attacks, achieving high confidentiality and integrity impacts with a changed scope, allowing the attacker to steal sensitive data or impersonate users in a cross-origin context.
Mitigation guidance is available in the Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21264.
Details
- CWE(s)