CVE-2026-1436: Graylog API Auth Bypass Vulnerability

CVE-2026-1436 Overview

CVE-2026-1436 is an Insecure Direct Object Reference (IDOR) vulnerability in the Graylog API version 2.2.3. The vulnerability occurs when an authenticated user modifies the user ID parameter in the API URL, allowing unauthorized access to other users' profiles. The affected endpoint /users/<user_id> fails to implement proper object-level authorization checks, enabling any authenticated user to enumerate valid system users and access sensitive information including names, email addresses, internal identifiers, and last activity timestamps.

Critical Impact

Authenticated users can access sensitive profile information of all other users in the Graylog system, leading to information disclosure and potential privacy violations.

Affected Products

• Graylog version 2.2.3
• Graylog REST API v2

Discovery Timeline

• 2026-02-18 - CVE-2026-1436 published to NVD
• 2026-02-18 - Last updated in NVD database

Technical Details for CVE-2026-1436

Vulnerability Analysis

This IDOR vulnerability exists in the Graylog REST API's user management functionality. The core issue is the absence of object-level authorization validation when processing requests to the user profile endpoint. When an authenticated user sends a request to retrieve user information, the API accepts any user identifier without verifying whether the requesting user has permission to access that specific resource.

The vulnerable endpoint http://<IP>:12900/users/<my_user> accepts a user identifier as a path parameter but only validates that the request comes from an authenticated user—not that the authenticated user has authorization to view the requested profile. This architectural flaw allows horizontal privilege escalation where any low-privileged authenticated user can access data belonging to other users, including administrators.

The information exposed includes personally identifiable information (PII) such as full names, email addresses, internal user identifiers, and activity metadata. This data could be leveraged for social engineering attacks, targeted phishing campaigns, or reconnaissance for further exploitation of the system.

Root Cause

The root cause is a missing authorization check at the object level (CWE-639: Authorization Bypass Through User-Controlled Key). The application authenticates the user making the request but fails to validate whether that user is authorized to access the specific resource identified in the URL path. The user-controlled user_id parameter is trusted without verification against the authenticated user's permissions.

Attack Vector

The attack is network-accessible and requires low-privilege authenticated access to the Graylog system. An attacker with valid credentials can simply enumerate user IDs by modifying the URL path parameter in requests to the /users/ endpoint. The attack requires no user interaction and can be automated to systematically extract information about all users in the system.

The exploitation process involves:

1. Authenticating to the Graylog system with valid credentials
2. Making a legitimate request to view one's own profile at /users/<attacker_user>
3. Modifying the user identifier in the URL to target other users
4. Iterating through possible user identifiers to enumerate all accounts and extract their profile data

Since no code examples are available from verified sources, readers should consult the INCIBE Security Notice for technical details on the vulnerability mechanism.

Detection Methods for CVE-2026-1436

Indicators of Compromise

• Unusual volume of API requests to the /users/ endpoint from a single authenticated session
• Sequential or pattern-based access to multiple user profiles in short time windows
• API access logs showing requests to user profiles that don't match the authenticated user's identity
• Failed and successful requests indicating enumeration attempts across user identifiers

Detection Strategies

• Implement API request monitoring to detect anomalous access patterns to user profile endpoints
• Enable detailed audit logging for all user management API calls with correlation to authenticated sessions
• Deploy web application firewall (WAF) rules to detect and alert on suspicious parameter manipulation patterns
• Configure behavioral analytics to identify users accessing resources outside their normal scope

Monitoring Recommendations

• Monitor Graylog API access logs at port 12900 for unusual request patterns
• Set up alerts for single users accessing multiple distinct user profiles within configurable time thresholds
• Correlate API access logs with authentication events to identify discrepancies
• Review periodic reports of user profile access to detect unauthorized information gathering

How to Mitigate CVE-2026-1436

Immediate Actions Required

• Upgrade Graylog to the latest patched version that addresses this vulnerability
• Restrict network access to the Graylog API (port 12900) to authorized administrative networks only
• Review API access logs for potential prior exploitation and unauthorized user enumeration
• Consider implementing additional authentication requirements for sensitive user management endpoints

Patch Information

Users should upgrade to a patched version of Graylog that implements proper object-level authorization checks. Consult the INCIBE Security Notice for specific patch details and vendor guidance on remediation.

Workarounds

• Implement network segmentation to restrict API access to trusted administrative networks only
• Configure reverse proxy or API gateway with additional authorization validation before requests reach Graylog
• Enable enhanced logging and monitoring to detect exploitation attempts while awaiting patch deployment
• Consider temporarily disabling external API access if not required for operations

# Example: Restrict access to Graylog API using iptables
iptables -A INPUT -p tcp --dport 12900 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 12900 -j DROP