CVE-2026-81846: runZero Platform Authorization Bypass Flaw

CVE-2026-81846 Overview

CVE-2026-81846 is an authorization bypass vulnerability in the runZero Platform Model Context Protocol (MCP) service. The flaw is classified as CWE-639: Authorization Bypass Through User-Controlled Key. An authenticated attacker with low privileges can leverage a user-controlled key to access findings and summaries data belonging to other tenants or users. runZero resolved the issue in version 5.1.260826.0. The exposure is limited to confidentiality of MCP-served data. No integrity or availability impact has been reported. See the runZero Advisory for CVE-2026-81846 for vendor details.

Critical Impact
Authenticated users can bypass authorization checks in the runZero MCP service and read findings and summaries data outside their intended scope.

Affected Products

runZero Platform MCP service versions prior to 5.1.260826.0
runZero Platform (hosted and self-hosted deployments exposing the MCP service)
Downstream AI assistants and tooling integrated with the runZero MCP service

Discovery Timeline

2026-09-01 - CVE-2026-81846 published to NVD
2026-09-01 - Last updated in NVD database
Fixed in - runZero Platform version 5.1.260826.0 (release notes)

Technical Details for CVE-2026-81846

Vulnerability Analysis

The runZero Platform exposes an MCP service so that AI assistants and automation can query findings and summaries. The service accepts a client-supplied identifier when retrieving records. Prior to the fix, the MCP handlers did not enforce that the caller was authorized for the object referenced by that identifier.

An authenticated caller with a valid session can therefore substitute an identifier belonging to another user or organizational scope. The service returns the requested findings or summary records without validating ownership. The exposure is confidentiality only; the vulnerability does not permit modification or service disruption. Exploitation requires an authenticated account and knowledge or enumeration of target identifiers, which is reflected in the higher attack complexity noted by the vendor.

Root Cause

The root cause is a missing authorization check on a user-controlled key in the MCP request path, matching the CWE-639 pattern. The service trusted the caller-supplied object identifier and mapped it to backend records without verifying that the authenticated principal owned or had scope to the referenced object. Authorization decisions were effectively delegated to a client-controlled parameter.

Attack Vector

The vulnerability is exploitable over the network by an authenticated user against the runZero MCP endpoint. The attacker issues an MCP request for findings or summaries and supplies an identifier belonging to a different account or scope. The server returns the record. No user interaction is required beyond the attacker's own MCP client. Refer to the runZero advisory for the definitive technical description.

Detection Methods for CVE-2026-81846

Indicators of Compromise

MCP service requests from a single authenticated principal enumerating sequential or unrelated finding and summary identifiers.
Successful MCP responses returning objects whose owning tenant or user does not match the requesting session.
Spikes in MCP query volume from a single API token or session outside of established baselines.

Detection Strategies

Correlate MCP request logs with the authenticated principal and the owner of the returned object to flag cross-scope access.
Alert on high-cardinality identifier access patterns from one caller within a short window.
Compare pre-upgrade and post-upgrade MCP access logs to identify historical cross-tenant reads.

Monitoring Recommendations

Enable verbose audit logging on the runZero MCP service and forward events to a centralized log store.
Track per-token access rates and unique identifiers requested against MCP endpoints.
Review API tokens with MCP scope and rotate any tokens with anomalous access history since the vulnerability was introduced.

How to Mitigate CVE-2026-81846

Immediate Actions Required

Upgrade the runZero Platform to version 5.1.260826.0 or later, per the runZero release notes.
Audit MCP access logs for cross-scope reads of findings and summaries prior to the upgrade.
Rotate API tokens and MCP client credentials that predate the patched build.

Patch Information

runZero resolved CVE-2026-81846 in Platform version 5.1.260826.0. The patch enforces authorization checks on MCP requests so that user-supplied identifiers cannot be used to reference objects outside the authenticated principal's scope. Hosted runZero customers receive the fix automatically. Self-hosted deployments must apply the update.

Workarounds

Disable or network-restrict the runZero MCP service until the upgrade to 5.1.260826.0 is applied.
Limit MCP access to a small set of trusted service accounts and remove broad token issuance.
Restrict inbound access to the MCP endpoint using firewall or reverse-proxy allowlists tied to known clients.

bash

# Verify the installed runZero Platform version includes the fix
curl -sS https://<runzero-host>/api/v1.0/version \
  -H "Authorization: Bearer $RUNZERO_TOKEN"

# Expected: version >= 5.1.260826.0