EUVD-2025-5949

Comprehensive Technical Analysis of EUVD-2025-5949

1. Vulnerability Assessment and Severity Evaluation

The vulnerability described in EUVD-2025-5949 is a Buffer Overflow in the CGI parser's handling of the "Content-Length" header of HTTP POST requests. This vulnerability affects multiple models and versions of DrayTek Vigor routers. The CVSS (Common Vulnerability Scoring System) base score of 9.8 indicates a critical severity level. The CVSS vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H breaks down as follows:

• AV:N (Attack Vector: Network) - The vulnerability is exploitable remotely over the network.
• AC:L (Attack Complexity: Low) - The attack requires minimal skill or resources.
• PR:N (Privileges Required: None) - No privileges are required to exploit the vulnerability.
• UI:N (User Interaction: None) - No user interaction is required for the attack to succeed.
• S:U (Scope: Unchanged) - The vulnerability does not change the security scope.
• C:H (Confidentiality: High) - The vulnerability can lead to a complete breach of confidentiality.
• I:H (Integrity: High) - The vulnerability can lead to a complete breach of integrity.
• A:H (Availability: High) - The vulnerability can lead to a complete breach of availability.

2. Potential Attack Vectors and Exploitation Methods

The primary attack vector is through crafted HTTP POST requests with a malicious "Content-Length" header. An attacker can send these requests to the vulnerable CGI parser, causing a buffer overflow. This overflow can lead to arbitrary code execution, allowing the attacker to:

• Gain unauthorized access to the router.
• Execute commands with elevated privileges.
• Compromise the integrity and confidentiality of data.
• Disrupt network services.

3. Affected Systems and Software Versions

The vulnerability affects the following DrayTek Vigor router models and firmware versions:

• Vigor2620/LTE200: 3.9.8.9 and earlier
• Vigor2860/2925: 3.9.8 and earlier
• Vigor2862/2926: 3.9.9.5 and earlier
• Vigor2133/2762/2832: 3.9.9 and earlier
• Vigor165/166: 4.2.7 and earlier
• Vigor2135/2765/2766: 4.4.5.1 and earlier
• Vigor2865/2866/2927: 4.4.5.3 and earlier
• Vigor2962/3910: 4.3.2.8/4.4.3.1 and earlier
• Vigor3912: 4.3.6.1 and earlier

4. Recommended Mitigation Strategies

1. Firmware Update: Immediately update the firmware of affected routers to the latest version provided by DrayTek.
2. Network Segmentation: Isolate vulnerable routers from critical network segments to limit potential damage.
3. Firewall Rules: Implement strict firewall rules to restrict access to the router's management interface.
4. Intrusion Detection/Prevention Systems (IDS/IPS): Deploy IDS/IPS to monitor and block suspicious HTTP POST requests.
5. Regular Audits: Conduct regular security audits and vulnerability assessments to identify and mitigate similar issues.

5. Impact on European Cybersecurity Landscape

The widespread use of DrayTek routers in both enterprise and consumer environments across Europe makes this vulnerability particularly concerning. Successful exploitation could lead to significant disruptions in network services, data breaches, and potential financial losses. Organizations and individuals relying on these routers for critical operations are at risk, underscoring the need for prompt mitigation and enhanced cybersecurity measures.

6. Technical Details for Security Professionals

• Exploitation Details: The vulnerability is triggered by sending an HTTP POST request with a specially crafted "Content-Length" header. The CGI parser fails to properly validate the length, leading to a buffer overflow.
• Detection: Security professionals can detect exploitation attempts by monitoring network traffic for anomalous HTTP POST requests targeting the router's management interface.
• Mitigation: Implementing a Web Application Firewall (WAF) can help filter out malicious HTTP requests. Additionally, ensuring that routers are not exposed to the public internet without proper security controls is crucial.
• Incident Response: In case of a suspected breach, isolate the affected router, conduct a forensic analysis to determine the extent of the compromise, and apply necessary patches and updates.

Conclusion

EUVD-2025-5949 represents a critical vulnerability affecting multiple DrayTek Vigor router models. The potential for remote code execution and the ease of exploitation make it a high-priority issue for cybersecurity professionals. Immediate action, including firmware updates and enhanced security measures, is essential to mitigate the risk and protect European networks from potential attacks.