CVE-2026-21226
Published: 13 January 2026
Summary
CVE-2026-21226 is a high-severity Deserialization of Untrusted Data (CWE-502) vulnerability in Microsoft Azure Core Shared Client Library. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked in the top 21.1% of CVEs by exploit likelihood; 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-2 (Flaw Remediation).
Deeper analysis
CVE-2026-21226 is a deserialization of untrusted data vulnerability, tracked under CWE-502, that affects the Azure Core shared client library for Python. The flaw carries a CVSS 3.1 score of 7.5 and permits an authorized attacker to execute arbitrary code over a network.
An attacker with limited privileges can exploit the issue remotely, though successful exploitation requires high attack complexity and no user interaction. Successful attacks result in high impact to confidentiality, integrity, and availability on the affected system.
The Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21226 provides the authoritative source for mitigation guidance and any available patches. The associated EPSS score has remained flat at 0.0270 with no material increase since disclosure.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2009
Vulnerability details
Deserialization of untrusted data in Azure Core shared client library for Python allows an authorized attacker to execute code over a network.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Deserialization of untrusted data (CWE-502) in a network-accessible Python library directly enables remote code execution, mapping to public-facing app exploitation (T1190), client-side exploitation for execution (T1203), and Python command interpreter usage (T1059.006).
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Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly remediates the deserialization flaw in the Azure Core Python library by requiring identification, reporting, and correction of the specific vulnerability.
Prevents exploitation by validating untrusted network inputs at deserialization points in the client library to reject malformed or malicious data.
Mitigates remote code execution from deserialization by implementing memory protections that prevent unauthorized code from executing.