CVE-2017-17537 in RouterBOARD
Summary
by MITRE
MikroTik RouterBOARD v6.39.2 and v6.40.5 allows an unauthenticated remote attacker to cause a denial of service by connecting to TCP port 53 and sending data that begins with many '\0' characters, possibly related to DNS.
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Analysis
by VulDB Data Team • 12/15/2019
The vulnerability identified as CVE-2017-17537 affects MikroTik RouterBOARD devices running firmware versions 6.39.2 and 6.40.5, presenting a significant remote denial of service risk that can be exploited by unauthenticated attackers. This flaw specifically targets the device's handling of DNS-related traffic on TCP port 53, where the system fails to properly validate incoming data sequences. The vulnerability manifests when an attacker sends specially crafted data packets that begin with multiple null characters, which triggers an abnormal processing behavior in the router's DNS service implementation. This issue represents a classic example of improper input validation where the system does not adequately sanitize or reject malformed data before processing, leading to resource exhaustion or system instability.
The technical exploitation of this vulnerability leverages the DNS service's insufficient data validation mechanisms, specifically targeting the TCP port 53 which is traditionally used for DNS queries. When the router receives data containing numerous null characters at the beginning of a TCP connection, the system's processing logic fails to properly handle this malformed input, resulting in a cascading failure that can cause the device to become unresponsive or crash entirely. This behavior aligns with CWE-20, which describes improper input validation, and demonstrates how seemingly benign data patterns can trigger critical system failures when not properly sanitized. The attack requires no authentication credentials and can be executed from any network location, making it particularly dangerous in network environments where such devices are exposed to untrusted traffic.
The operational impact of this vulnerability extends beyond simple service disruption, as it can render network infrastructure completely inaccessible to legitimate users and administrators. When exploited successfully, the denial of service condition affects not only the DNS functionality but can also potentially impact other network services running on the same device, as the system's stability is compromised. Network administrators may experience complete loss of connectivity to the affected router, requiring manual intervention to restore service, including device rebooting or firmware updates. This vulnerability particularly affects enterprise and organizational networks where MikroTik devices serve as critical network infrastructure components, potentially causing widespread disruption to business operations and network availability. The impact is compounded by the fact that many organizations may not actively monitor or patch these devices regularly, leaving them vulnerable to exploitation.
Mitigation strategies for CVE-2017-17537 should prioritize immediate firmware updates to versions that address the DNS input validation issue, as provided by MikroTik in subsequent releases. Network segmentation and access control measures should be implemented to restrict direct access to TCP port 53 from untrusted networks, effectively blocking potential exploitation attempts. Additionally, implementing network monitoring solutions that can detect unusual traffic patterns or malformed DNS requests can provide early warning of attempted exploitation. Organizations should also consider disabling unnecessary DNS services when not required and establishing robust patch management processes to ensure timely deployment of security updates. The vulnerability highlights the importance of validating all network input and demonstrates how basic protocol implementations can become attack vectors when proper input sanitization is not enforced, making it a critical consideration for network security hardening efforts.