Microsoft MCP Gateway: Authorization bypass leading to privilege escalation
Summary
Microsoft MCP Gateway (mcp-gateway) contains an authorization bypass caused by a user-controlled key (CWE-639). An authorized attacker on the network with a low-privilege account can elevate privileges, with high impact on confidentiality, integrity and availability. No user interaction is required. The affected version range and the fixed build could not be verified at the time of writing.
Affected
- Microsoft mcp-gateway, as listed in the CVE record: "from 1.0.0.0 before 1.0.0" (internally contradictory, unverified)
- Platform listed in the CVE record: x64-based systems
Fixed in
Unknown. Check the Microsoft advisory for the fixed build.
Workaround
- None published that could be verified.
- Interim hardening until a fix is confirmed: restrict access to the gateway, limit accounts with gateway access, review logs for unusual resource access, and make sure development-only authentication handlers are disabled outside development.
Exploitation
- No active exploitation known at the time of writing. A third-party source lists it as not in KEV.
- No public proof of concept found.
- CISA SSVC: exploitation none, automatable no, technical impact total.
Our recommendation
- Check whether MCP Gateway is deployed in your environment, including containers, Kubernetes or Azure services.
- Confirm the fixed build in the Microsoft advisory and patch promptly.
- Restrict network access to the gateway and review accounts that can reach it.
- Monitor logs for unusual resource access.
Information from Microsoft (Patch Tuesday November 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide (MSRC) msrc.microsoft.com
- CVE Record (CVE Program) www.cve.org
- Strix CVE summary (third party) www.strix.ai
- Microsoft November 2026 Patch Tuesday coverage (Cybersecurity News) cybersecuritynews.com
- MCP Gateway security documentation (DeepWiki, third party) deepwiki.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 10 Nov 2026, 23:55.
Original description (NVD)
Authorization bypass through user-controlled key in Microsoft MCP Gateway allows an authorized attacker to elevate privileges over a network.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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