Live Exposure Defense: From CVE to Confirmed Exposure in 12 Hours – See more

Back
New CVE Detected

CVE-2026-81091 – SSRF via Caller-Supplied Target URL – mcp-use Inspector (mcp-use) ≤2.3.2

Be the first to know when new zero-days emerge:

Subscribe to Email Alerts
Subscribe to RSS Feed

Summary

CVE-2026-81091 is a Server-Side Request Forgery (SSRF) vulnerability in the proxy middleware of the mcp-use Inspector. The mountMcpProxy function forwards requests to a caller-supplied destination without validating whether that destination is a private, loopback, or link-local address, and does not re-validate redirect targets. This allows an unauthenticated network attacker to make the Inspector server issue requests to internal-only addresses and read back the responses, and the issue is rated HIGH severity.

Technical details

  • Root cause: mountMcpProxy reads the proxy target from the X-Target-URL header or the __mcp_target parameter and forwards the request without validating that the destination is not a private, loopback, or link-local address.
  • Trigger conditions: An attacker sends a request to the exposed Inspector proxy endpoint specifying an internal or restricted address as the target; the server also fails to re-apply validation when the initial response is a redirect, allowing the redirect to point to a disallowed address.
  • Attack vector: Network-based, no authentication or user interaction required (AV:N, PR:N, UI:N).
  • Impact: Confidentiality impact — the attacker can make the host issue requests to internal-only network resources and read the returned responses, potentially exposing internal services, cloud metadata endpoints, or other network-restricted resources.

Affected software

  • mcp-use (Inspector proxy component): versions 0 through 2.3.2 (semver)

Severity

  • CVSS v3.1: 8.6 (HIGH) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
  • CVSS v4.0: 8.7 (HIGH) — CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade mcp-use to a release beyond 2.3.2 that includes the fix (see the GitHub Security Advisory GHSA-f2jg-rm2x-hc5p and the mcp-use repository for the specific patched release).
  • If no patch is available yet: Do not expose the Inspector proxy endpoint to untrusted networks; restrict access to the Inspector interface to trusted/internal users only; block outbound requests from the Inspector host to private, loopback, and link-local address ranges (e.g., via network egress controls); disable or remove the proxy feature if it is not required.

References

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report

How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report
Close

Subscribe to Threat Center RSS

Copy/paste the link below into your preferred RSS reader or follow these instructions to subscribe to Slack alerts.

Open RSS feedSlack setup instructions

Close

Get Real-Time CVE Alerts to Your Email

Be the first to know when new zero-days emerge