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 17.6% 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).
Threat & Defense at a Glance
Threat & Defense Details
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.
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).
NVD Description
Deserialization of untrusted data in Azure Core shared client library for Python allows an authorized attacker to execute code over a network.
Deeper analysisAI
CVE-2026-21226, published on 2026-01-13, is a deserialization of untrusted data vulnerability (CWE-502) affecting the Azure Core shared client library for Python. The issue enables an authorized attacker to execute code over a network, with a CVSS v3.1 base score of 7.5 (AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H).
An attacker with low privileges (PR:L) can exploit this vulnerability remotely over the network (AV:N), though it requires high attack complexity (AC:H) and no user interaction (UI:N). Successful exploitation allows high-impact consequences, including unauthorized access to confidential data, modification of system integrity, and disruption of availability, without changing the scope (S:U).
The Microsoft Security Response Center advisory provides further details on this vulnerability, including mitigation guidance, at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21226.
Details
- CWE(s)