EUVD-2026-11416

Comprehensive Technical Analysis of EUVD-2026-11416

1. Vulnerability Assessment and Severity Evaluation

Vulnerability Description: The vulnerability in AdGuard Home, a network-wide ad and tracking blocker, allows an unauthenticated remote attacker to bypass authentication mechanisms. This is achieved by sending an HTTP/1.1 request that requests an upgrade to HTTP/2 cleartext (h2c). Once the upgrade is accepted, the resulting HTTP/2 connection is handled without any authentication middleware, allowing the attacker to execute fully authenticated requests.

Severity Evaluation:

• Base Score: 9.8
• Base Score Version: 3.1
• Base Score Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

The CVSS score of 9.8 indicates a critical vulnerability. The high severity is due to the following factors:

• Attack Vector (AV:N): The vulnerability is exploitable over the network.
• Attack Complexity (AC:L): The attack requires low complexity.
• Privileges Required (PR:N): No privileges are required to exploit the vulnerability.
• User Interaction (UI:N): No user interaction is required.
• Scope (S:U): The vulnerability does not change the security scope.
• Confidentiality (C:H), Integrity (I:H), Availability (A:H): The vulnerability has a high impact on confidentiality, integrity, and availability.

2. Potential Attack Vectors and Exploitation Methods

Attack Vectors:

• Network-Based Attack: An attacker can exploit this vulnerability remotely over the network.
• HTTP/2 Cleartext Upgrade: The attacker sends an HTTP/1.1 request with an upgrade header to HTTP/2 cleartext (h2c).

Exploitation Methods:

• Authentication Bypass: Once the HTTP/2 connection is established, the attacker can send authenticated requests without providing any credentials.
• Data Exfiltration: The attacker can access and exfiltrate sensitive data.
• Configuration Changes: The attacker can modify the configuration settings of AdGuard Home.
• Service Disruption: The attacker can disrupt the service by sending malicious requests.

3. Affected Systems and Software Versions

Affected Software:

• AdGuard Home versions prior to 0.107.73.

Affected Systems:

• Any system running the vulnerable versions of AdGuard Home.
• Networks where AdGuard Home is deployed as a network-wide ad and tracking blocker.

4. Recommended Mitigation Strategies

Immediate Actions:

• Update Software: Upgrade AdGuard Home to version 0.107.73 or later.
• Network Segmentation: Isolate AdGuard Home from public networks to limit exposure.
• Firewall Rules: Implement firewall rules to block unauthorized access to the AdGuard Home interface.

Long-Term Strategies:

• Regular Patching: Ensure that all software, including AdGuard Home, is regularly updated and patched.
• Monitoring and Logging: Implement robust monitoring and logging to detect and respond to suspicious activities.
• Access Controls: Enforce strict access controls and authentication mechanisms.

5. Impact on European Cybersecurity Landscape

Potential Impact:

• Widespread Adoption: AdGuard Home is widely used in Europe for network-wide ad and tracking blocking. This vulnerability could lead to widespread exploitation.
• Data Breaches: Sensitive data could be compromised, leading to data breaches and potential GDPR violations.
• Service Disruption: Critical services relying on AdGuard Home could be disrupted, affecting business operations.

Regulatory Compliance:

• GDPR: Organizations must ensure that they comply with GDPR regulations by protecting personal data and reporting breaches promptly.
• NIS Directive: Critical infrastructure providers must adhere to the Network and Information Systems (NIS) Directive to ensure the security and resilience of their networks.

6. Technical Details for Security Professionals

Technical Overview:

• HTTP/2 Cleartext Upgrade: The vulnerability leverages the HTTP/2 cleartext (h2c) upgrade mechanism. When an HTTP/1.1 request with an upgrade header is sent, the server accepts the upgrade and handles the resulting HTTP/2 connection without authentication middleware.
• Authentication Middleware: The inner mux handling the HTTP/2 connection lacks authentication middleware, allowing unauthenticated requests to be processed as authenticated.

Detection and Response:

• Intrusion Detection Systems (IDS): Implement IDS to detect suspicious HTTP/2 upgrade requests.
• Log Analysis: Analyze logs for unusual HTTP/2 upgrade requests and subsequent authenticated actions.
• Incident Response: Develop an incident response plan to quickly identify and mitigate any exploitation attempts.

Conclusion: The vulnerability in AdGuard Home (EUVD-2026-11416) is critical and requires immediate attention. Organizations should prioritize updating to the patched version and implement robust security measures to protect against potential exploitation. The impact on the European cybersecurity landscape underscores the importance of proactive security management and compliance with regulatory requirements.