CVE-2020-24376 in Freebox Server
Summary
by MITRE
A DNS rebinding vulnerability in the UPnP IGD implementations in Freebox Server before 4.2.3.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 09/17/2020
The vulnerability identified as CVE-2020-24376 represents a critical DNS rebinding flaw affecting Universal Plug and Play Internet Gateway Device implementations within Freebox Server versions prior to 4.2.3. This vulnerability resides in the network device's handling of DNS responses and can be exploited by remote attackers to bypass security boundaries and gain unauthorized access to internal network resources. The issue stems from improper validation of DNS responses during UPnP service discovery processes, creating an attack surface that allows malicious actors to manipulate network traffic routing and access protected internal services.
The technical flaw manifests in the UPnP IGD implementation where the system fails to properly validate DNS responses received from external sources. When a device attempts to discover UPnP services on the network, the implementation does not adequately verify the authenticity or origin of DNS records returned by external servers. This allows attackers to perform DNS rebinding attacks by controlling DNS resolution responses, effectively enabling them to redirect traffic intended for external services to internal network addresses. The vulnerability operates at the network layer and can be classified under CWE-611 Improper Restriction of XML External Entity Reference, though more specifically aligns with CWE-284 Improper Access Control in network service contexts. The attack vector leverages the DNS rebinding technique where an attacker controls DNS responses to make a client believe it is communicating with different hosts, enabling unauthorized access to internal services.
The operational impact of this vulnerability extends beyond simple network disruption to potentially enable full network compromise. Attackers can leverage this vulnerability to bypass firewall rules and access internal services that should normally be restricted from external access, including but not limited to web interfaces, administrative portals, and network management services. The attack can be executed from any location with access to the internet, making it particularly dangerous for home and small office network environments where Freebox devices are commonly deployed. This vulnerability directly maps to several ATT&CK techniques including T1071.004 Application Layer Protocol DNS and T1068 Valid Accounts, as attackers can use the compromised service to escalate privileges and move laterally within the network. The exposure of internal services can lead to complete network compromise, data exfiltration, and potential botnet recruitment.
Mitigation strategies for this vulnerability require immediate firmware updates to Freebox Server versions 4.2.3 and later, which contain proper DNS validation mechanisms and improved UPnP service handling. Network administrators should implement additional protective measures including DNS filtering, firewall rules to restrict UPnP traffic, and network segmentation to limit the impact of potential exploitation. The implementation of DNS security extensions and proper DNS response validation should be enforced at the network level to prevent similar vulnerabilities in other devices. Organizations should also conduct comprehensive network audits to identify other potentially vulnerable UPnP implementations and ensure proper access controls are in place. Regular security assessments and vulnerability scanning should include checks for UPnP service exposure and proper DNS handling to prevent exploitation of similar vulnerabilities in other network infrastructure components.