PatchSiren cyber security CVE debrief

CVE-2026-40411 Microsoft CVE debrief

A critical vulnerability in Azure Virtual Network Gateway permits network-based code execution by authenticated attackers. The flaw stems from improper input validation (CWE-20). Microsoft has acknowledged this issue via their Security Response Center. The CVSS 3.1 vector (AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H) indicates network attack vector, low complexity, low privileges required, no user interaction, and changed scope with high impact across confidentiality, integrity, and availability. The vulnerability was published to NVD on 22 May 2026 and modified on 26 May 2026; it remains under analysis with no known exploitation in ransomware campaigns and no KEV listing.

Vendor: Microsoft
Product: Azure Virtual Network Gateway
CVSS: CRITICAL 9.9
CISA KEV: Not listed in stored evidence
Original CVE published: 2026-05-22
Original CVE updated: 2026-05-27
Advisory published: 2026-05-22
Advisory updated: 2026-05-27

Who should care

Organizations operating Azure Virtual Network Gateways for hybrid connectivity, site-to-site VPN, or ExpressRoute; cloud security teams managing Azure network infrastructure; incident response teams tracking Azure service vulnerabilities

Technical summary

The vulnerability exists in Azure Virtual Network Gateway's handling of network input, where insufficient validation allows an attacker with low privileges to execute arbitrary code. The attack requires network access but no user interaction, with potential for scope change affecting resources beyond the initial security boundary. The critical CVSS score (9.9) reflects severe impact across all security dimensions.

Defensive priority

critical

Recommended defensive actions

Review Microsoft Security Response Center guidance for CVE-2026-40411 for patch availability and deployment timelines
Assess Azure Virtual Network Gateway deployments for exposure to network-accessible attack paths
Apply network segmentation controls to limit lateral movement potential if patching is delayed
Monitor Azure Service Health and Microsoft Security Update Guide for configuration or mitigation guidance
Validate input sanitization on custom integrations with Azure Virtual Network Gateway APIs

Evidence notes

Vendor attribution to Microsoft is inferred from reference domain (msrc.microsoft.com) with low confidence; the CVE description specifies Azure Virtual Network Gateway as the affected product. No CPE criteria were available in the source record.

Official resources

Microsoft MSRC