What is the CVSS score of CVE-2026-21531?

CVE-2026-21531 has a CVSS 3.1 base score of 9.8 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.3%.

Which versions of Azure are affected by CVE-2026-21531?

Azure Conversation Authoring Client Library versions up to 1.0.0 contain a critical deserialization vulnerability (CVSS 9.8) that could allow attackers to execute arbitrary code on systems using this…. A patch is available.

How to fix or mitigate CVE-2026-21531?

Within 24 hours: Identify all applications and systems using Azure Conversation Authoring Client Library up to version 1.0.0 and document their criticality and exposure. Within 7 days: Implement network segmentation to isolate affected systems, restrict inbound connections to trusted sources only, and monitor for exploitation attempts. Within 30 days: Establish a patch readiness plan with Microsoft, consider alternative libraries if available, and prepare emergency response procedures; conduct immediate security testing once patches are released.

Azure CVE-2026-21531

CRITICAL

Deserialization of Untrusted Data (CWE-502)

2026-02-10 secure@microsoft.com

GHSA-436v-jg82-p533

Azure Deserialization Azure Conversation Authoring Client Library

9.8

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

9.8 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Patch released

Mar 31, 2026 - 21:13 nvd

Patch available

Analysis Generated

Mar 12, 2026 - 22:02 vuln.today

CVE Published

Feb 10, 2026 - 18:16 nvd

CRITICAL 9.8

DescriptionCVE.org

Deserialization of untrusted data in Azure SDK allows an unauthorized attacker to execute code over a network.

AnalysisAI

Deserialization of untrusted data in Azure SDK allows unauthorized code execution over a network. EPSS 0.32%.

Unlock full vulnerability intelligence

Risk assessment & exploitation conditions
Attack chain visualization
Remediation with exact patch versions
Threat intelligence from 22 sources
Personal watchlist & email alerts

Continue with Google Continue with GitHub

Free forever · No credit card required

Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access

Craft malicious serialized object

Exploit

Send to Azure SDK deserialization endpoint

Execution

Trigger unsafe deserialization

Impact

Execute arbitrary code

Access

Craft malicious serialized object

Exploit

Send to Azure SDK deserialization endpoint

Execution

Trigger unsafe deserialization

Impact

Execute arbitrary code

Vulnerability AssessmentAI

Exploitation	No special conditions — remote unauthenticated exploitation against Azure SDK deserialization functions accepting untrusted serialized data over the network. Additional conditions and limiting factors are described in the full assessment.
Risk Assessment	CVSS 9.8. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario	Attacker sends serialized payload to application using Azure SDK, achieving code execution through unsafe deserialization.
Remediation	Update Azure SDK to patched version. Detailed patch versions, workarounds, and compensating controls in full report.

Recommended ActionAI

Within 24 hours: Identify all applications and systems using Azure Conversation Authoring Client Library up to version 1.0.0 and document their criticality and exposure. …

Threat intelligence, references, and detailed analysis are available after sign-in.

CVE-2026-21531 vulnerability details – vuln.today

Back

Azure CVE-2026-21531

Severity by source

CVSS VectorNVD

Lifecycle Timeline

DescriptionCVE.org

AnalysisAI

Unlock full vulnerability intelligence

Attack ChainAIDerived

Vulnerability AssessmentAI

Recommended ActionAI

Share

External POC / Exploit Code