CVE-2026-21532: Azure Function Information Disclosure

CVE-2026-21532 Overview

CVE-2026-21532 is an Information Disclosure vulnerability affecting Microsoft Azure Functions. This vulnerability allows unauthenticated attackers to access sensitive information through network-based attacks without requiring user interaction. The weakness, classified as CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor), could enable threat actors to obtain confidential data from affected Azure Function deployments.

Critical Impact

Attackers can exploit this vulnerability remotely without authentication to extract sensitive information from Azure Functions, potentially exposing configuration data, secrets, or other confidential resources with high impact to confidentiality.

Affected Products

• Microsoft Azure Functions

Discovery Timeline

• 2026-02-05 - CVE CVE-2026-21532 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2026-21532

Vulnerability Analysis

This Information Disclosure vulnerability in Azure Functions stems from improper handling of sensitive information (CWE-200). The vulnerability can be exploited remotely over the network with low attack complexity, requiring no privileges or user interaction. While the primary impact is unauthorized access to sensitive data, there is also a limited integrity impact that could allow minor unauthorized modifications.

The network-accessible nature of Azure Functions combined with the low barrier to exploitation makes this vulnerability particularly concerning for organizations with internet-facing serverless deployments. Successful exploitation could reveal environment variables, connection strings, application secrets, or internal configuration details that attackers could leverage for further attacks.

Root Cause

The root cause of CVE-2026-21532 is related to CWE-200: Exposure of Sensitive Information to an Unauthorized Actor. This weakness occurs when the Azure Function runtime inadvertently exposes sensitive information to actors who are not explicitly authorized to access that information. The exposure could occur through improper error handling, verbose logging, misconfigured endpoints, or other mechanisms that leak internal data to external parties.

Attack Vector

The attack vector for this vulnerability is network-based, allowing remote exploitation without authentication. An attacker can send specially crafted requests to vulnerable Azure Function endpoints to trigger the information disclosure condition. The attack does not require any user interaction, making it suitable for automated exploitation.

The vulnerability affects the confidentiality of data with high severity, while also presenting limited integrity concerns. Availability is not impacted. Attackers could potentially chain this information disclosure with other vulnerabilities to achieve more significant compromise of Azure-hosted applications and infrastructure.

Detection Methods for CVE-2026-21532

Indicators of Compromise

• Unusual outbound data transfers from Azure Function endpoints containing configuration or environment data
• Anomalous HTTP requests targeting Azure Function metadata endpoints or internal APIs
• Access logs showing repeated probing requests from external IP addresses targeting Function App resources
• Error responses containing verbose information that may indicate exploitation attempts

Detection Strategies

• Monitor Azure Function invocation logs for suspicious request patterns targeting internal endpoints
• Implement Web Application Firewall (WAF) rules to detect and block requests attempting information enumeration
• Enable Azure Monitor and Application Insights to track unusual data access patterns
• Review Azure Activity Logs for unauthorized access attempts to Function App configurations

Monitoring Recommendations

• Configure Azure Security Center alerts for anomalous Function App behavior
• Set up Log Analytics queries to identify information disclosure patterns in Function logs
• Enable diagnostic logging on all Azure Functions to capture detailed request/response information
• Implement SentinelOne Singularity Cloud Security for real-time detection of cloud-native threats

How to Mitigate CVE-2026-21532

Immediate Actions Required

• Apply the latest security updates from Microsoft for Azure Functions as soon as available
• Review Azure Function configurations to minimize exposed endpoints and remove unnecessary public access
• Enable Azure Functions authentication requirements to prevent anonymous access where possible
• Audit Function App settings for sensitive information that could be exposed

Patch Information

Microsoft has released a security update addressing this vulnerability. Organizations should review the Microsoft Security Update Guide for detailed patch information and apply the recommended updates to all affected Azure Function deployments.

For Azure Functions running on dedicated App Service Plans, ensure the underlying platform is updated. For Consumption Plan functions, Microsoft will apply backend updates automatically, but application-level configuration changes may still be required.

Workarounds

• Restrict network access to Azure Functions using Virtual Network integration and private endpoints
• Implement Azure API Management in front of Functions to add additional security controls
• Configure IP restrictions on Function Apps to limit access to known trusted IP ranges
• Enable Azure AD authentication to require identity verification for all Function invocations
• Review and minimize permissions granted to Function App managed identities

# Example: Configure IP restrictions for Azure Function App
az functionapp config access-restriction add \
  --resource-group <resource-group-name> \
  --name <function-app-name> \
  --rule-name "AllowTrustedIPs" \
  --action Allow \
  --ip-address <trusted-ip-range>/24 \
  --priority 100