Description
Multiple D-Link DSL gateway devices contain a command injection vulnerability in the dnscfg.cgi endpoint due to improper sanitization of user-supplied DNS configuration parameters. An unauthenticated remote attacker can inject and execute arbitrary shell commands, resulting in remote code execution. The affected endpoint is also associated with unauthenticated DNS modification (“DNSChanger”) behavior documented by D-Link, which reported active exploitation campaigns targeting firmware variants of the DSL-2740R, DSL-2640B, DSL-2780B, and DSL-526B models from 2016 through 2019. Exploitation evidence was observed by the Shadowserver Foundation on 2025-11-27 (UTC). Affected devices were declared end-of-life/end-of-service in early 2020.
EPSS Score:
1%
Comprehensive Technical Analysis of EUVD-2026-0944
1. Vulnerability Assessment and Severity Evaluation
The vulnerability described in EUVD-2026-0944 is a command injection flaw in the dnscfg.cgi endpoint of multiple D-Link DSL gateway devices. This vulnerability arises due to improper sanitization of user-supplied DNS configuration parameters, allowing an unauthenticated remote attacker to inject and execute arbitrary shell commands. The severity of this vulnerability is rated with a CVSS Base Score of 9.3, indicating a critical risk.
CVSS Base Score Vector Breakdown:
- Attack Vector (AV): Network (N) - The vulnerability is exploitable over the network.
- Attack Complexity (AC): Low (L) - The attack requires minimal skill or resources.
- Authentication (AT): None (N) - No authentication is required to exploit the vulnerability.
- Privileges Required (PR): None (N) - No special privileges are needed.
- User Interaction (UI): None (N) - No user interaction is required.
- Confidentiality Impact (VC): High (H) - Complete loss of confidentiality.
- Integrity Impact (VI): High (H) - Complete loss of integrity.
- Availability Impact (VA): High (H) - Complete loss of availability.
- Scope Change (SC): None (N) - The vulnerability does not change the security scope.
- Secondary Impact (SI): None (N) - No secondary impacts.
- Secondary Availability (SA): None (N) - No secondary availability impacts.
2. Potential Attack Vectors and Exploitation Methods
Attack Vectors:
- Unauthenticated Remote Command Injection: An attacker can send crafted HTTP requests to the
dnscfg.cgiendpoint with malicious DNS configuration parameters, leading to arbitrary command execution. - DNSChanger Behavior: The affected endpoint is also associated with unauthenticated DNS modification, allowing attackers to redirect traffic to malicious servers.
Exploitation Methods:
- Direct Exploitation: Attackers can directly exploit the vulnerability by sending specially crafted HTTP requests to the vulnerable endpoint.
- Automated Exploitation: Given the low complexity and lack of authentication requirements, automated scripts or bots can be used to scan for and exploit vulnerable devices en masse.
3. Affected Systems and Software Versions
The vulnerability affects the following D-Link DSL gateway models and firmware versions:
- DSL-2740R: Versions prior to 1.17
- DSL-2640B: Versions up to and including 1.07
- DSL-2780B: Versions up to and including 1.01.14
- DSL-526B: Versions up to and including 2.01
These devices were declared end-of-life/end-of-service in early 2020, meaning they no longer receive security updates.
4. Recommended Mitigation Strategies
Immediate Mitigation:
- Network Segmentation: Isolate affected devices from critical networks to limit potential damage.
- Firewall Rules: Implement strict firewall rules to block unauthorized access to the
dnscfg.cgiendpoint. - Monitoring: Increase monitoring of network traffic to detect and respond to suspicious activities.
Long-Term Mitigation:
- Device Replacement: Replace end-of-life devices with supported models that receive regular security updates.
- Firmware Updates: For devices still in use, ensure they are running the latest available firmware, even if it does not fully mitigate the vulnerability.
- Security Patches: Apply any available security patches or workarounds provided by D-Link or third-party security vendors.
5. Impact on European Cybersecurity Landscape
The widespread use of D-Link devices in both residential and small business environments poses a significant risk to the European cybersecurity landscape. The vulnerability's critical severity and the devices' end-of-life status exacerbate the risk, as many users may be unaware of the need to replace or update their devices. This can lead to large-scale exploitation, including DNS hijacking, data breaches, and potential integration into botnets for further malicious activities.
6. Technical Details for Security Professionals
Vulnerability Details:
- Endpoint:
dnscfg.cgi - Parameter: DNS configuration parameters
- Sanitization Issue: Improper sanitization allows for command injection.
Exploitation Steps:
- Identify Vulnerable Devices: Use network scanning tools to identify devices with the affected firmware versions.
- Craft Malicious Request: Create an HTTP request targeting the
dnscfg.cgiendpoint with malicious DNS configuration parameters. - Execute Command: Inject and execute arbitrary shell commands through the malicious request.
Detection and Response:
- Log Analysis: Monitor logs for unusual activity related to the
dnscfg.cgiendpoint. - Intrusion Detection Systems (IDS): Deploy IDS to detect and alert on suspicious network traffic.
- Incident Response: Have a predefined incident response plan to quickly address and mitigate any detected exploitation attempts.
References:
By understanding the technical details and implementing the recommended mitigation strategies, cybersecurity professionals can effectively manage the risk posed by this vulnerability and protect their networks from potential exploitation.