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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
2026-07-23
Advisory published
2026-05-22
Advisory updated
2026-07-23

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.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-40411 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-40411

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-40411 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-40411

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.