CVE-2026-25767: LavinMQ Auth Bypass Vulnerability

CVE-2026-25767 Overview

CVE-2026-25767 is a Broken Access Control vulnerability affecting LavinMQ, a high-performance message queue and streaming server. Before version 2.6.8, an authenticated user with the "Policymaker" tag could create shovels that bypass access controls, allowing unauthorized read and write access to messages across virtual hosts (vhosts) they should not have permission to access.

This vulnerability stems from insufficient authorization checks in the shovel configuration and definitions API endpoints. An attacker exploiting this flaw could read messages from unauthorized vhosts or publish messages to vhosts outside their permitted scope, potentially leading to data exfiltration, message tampering, or lateral movement within the message queue infrastructure.

Critical Impact

Authenticated users with Policymaker privileges can bypass vhost access controls to read or publish messages to unauthorized virtual hosts, compromising message queue isolation and data confidentiality.

Affected Products

• LavinMQ versions prior to 2.6.8

Discovery Timeline

• February 12, 2026 - CVE-2026-25767 published to NVD
• February 12, 2026 - Last updated in NVD database

Technical Details for CVE-2026-25767

Vulnerability Analysis

This vulnerability is classified as CWE-863: Incorrect Authorization. The core issue lies in how LavinMQ handled authorization checks for users with the "Policymaker" management tag when creating and configuring shovels.

Shovels in message queue systems are used to transfer messages between queues, potentially across different vhosts or even different servers. The vulnerable code paths allowed Policymaker users to configure shovels that could access vhosts beyond their authorized scope. This effectively breaks the multi-tenant isolation that vhosts are designed to provide.

The vulnerability is exploitable over the network by any authenticated user possessing the Policymaker tag. The attack requires low privileges (an authenticated session with specific management permissions) but no user interaction, making it relatively straightforward to exploit in environments where multiple users or tenants share a LavinMQ instance.

Root Cause

The root cause was insufficient authorization validation in two key areas:

1. Definitions API Endpoints: The /api/definitions/:vhost endpoints used refuse_unless_policymaker and refuse_unless_vhost_access checks, which were insufficient. Policymakers could access definition import/export functionality without full administrator privileges.

2. Shovel Configuration Validation: The shovel configuration logic did not properly validate that the user creating a shovel had access to both the source and destination vhosts specified in the shovel's URI configuration.

Attack Vector

An authenticated attacker with the Policymaker management tag could exploit this vulnerability by:

1. Authenticating to the LavinMQ management API with Policymaker credentials
2. Creating a shovel configuration that references a vhost the attacker is not authorized to access
3. Using the shovel to read messages from the unauthorized vhost (data exfiltration) or publish messages to it (message injection)

The security patches address this by requiring administrator privileges for definitions API operations and implementing proper validation of shovel configurations against the user's actual vhost permissions.

Security Patch - Definitions Controller (src/lavinmq/http/controller/definitions.cr):

 
         get "/api/definitions/:vhost" do |context, params|
           with_vhost(context, params) do |vhost|
-            refuse_unless_management(context, user(context), vhost)
-            refuse_unless_vhost_access(context, user(context), vhost)
+            refuse_unless_administrator(context, user(context))
             VHostDefinitions.new(@amqp_server, vhost).export(context.response)
           end
         end
 
         post "/api/definitions/:vhost" do |context, params|
           with_vhost(context, params) do |vhost|
-            refuse_unless_policymaker(context, user(context), vhost)
-            refuse_unless_vhost_access(context, user(context), vhost)
+            refuse_unless_administrator(context, user(context))
             body = parse_body(context)
             VHostDefinitions.new(@amqp_server, vhost).import(body)
           end
         end
 
         post "/api/definitions/:vhost/upload" do |context, params|
+          refuse_unless_administrator(context, user(context))
           with_vhost(context, params) do |vhost|
-            refuse_unless_policymaker(context, user(context), vhost)
-            refuse_unless_vhost_access(context, user(context), vhost)
             ::HTTP::FormData.parse(context.request) do |part|
               if part.name == "file"
                 body = JSON.parse(part.body)

Source: GitHub Commit 3a83e58

Security Patch - Shovel Configuration Validation (src/lavinmq/shovel/amqp_destination.cr):

 
       def initialize(@name : String, @uri : URI, @queue : String?, @exchange : String? = nil,
                      @exchange_key : String? = nil, @ack_mode = DEFAULT_ACK_MODE, direct_user : Auth::User? = nil)
-        unless @uri.user
+        if @uri.user.nil? && @uri.host.to_s.empty?
           if direct_user
             @uri.user = direct_user.name
             @uri.password = direct_user.plain_text_password

Source: GitHub Commit be03da3

Detection Methods for CVE-2026-25767

Indicators of Compromise

• Unexpected shovel configurations referencing vhosts that users should not have access to
• API requests to /api/definitions/:vhost endpoints from non-administrator users
• Unusual message flow patterns between vhosts that violate established access policies
• Audit log entries showing Policymaker users creating or modifying shovel configurations

Detection Strategies

• Monitor LavinMQ management API access logs for requests to definitions endpoints from users without administrator privileges
• Review existing shovel configurations for cross-vhost access patterns that may indicate exploitation
• Implement alerting on shovel creation events, particularly those involving multiple vhosts
• Audit user permissions to identify accounts with Policymaker tags that may have been used for exploitation

Monitoring Recommendations

• Enable detailed access logging for all LavinMQ management API endpoints
• Implement real-time monitoring of shovel creation and modification events
• Set up alerts for any definitions import/export operations performed by non-administrator users
• Review message queue access patterns to detect anomalous cross-vhost message transfers

How to Mitigate CVE-2026-25767

Immediate Actions Required

• Upgrade LavinMQ to version 2.6.8 or later immediately
• Audit all existing shovel configurations to identify any unauthorized cross-vhost access
• Review user accounts with Policymaker tags and verify they require this level of access
• Examine access logs for evidence of exploitation attempts or successful attacks

Patch Information

The vulnerability is fixed in LavinMQ version 2.6.8. The security patches align LavinMQ's permission model with RabbitMQ by requiring administrator privileges for definitions operations and implementing proper validation of shovel configurations.

For detailed technical information about the fix, see the GitHub Security Advisory GHSA-wh37-6vrr-r9wg.

Related pull requests:

• PR #1670 - Better validation of shovel config
• PR #1687 - Align permissions with RabbitMQ; require admin for definitions

Workarounds

• Restrict Policymaker tag assignments to only trusted administrators until patching is complete
• Implement network segmentation to limit access to the LavinMQ management API
• Use a web application firewall to block unauthorized access to /api/definitions/* and shovel-related endpoints
• Temporarily disable shovel functionality if not operationally required

# Verify LavinMQ version after upgrade
lavinmq --version
# Expected: 2.6.8 or higher

# Review existing shovel configurations
lavinmqctl list_shovels

# Audit users with Policymaker permissions
lavinmqctl list_users | grep policymaker