CVE-2018-4011 in Smart Firewall
Summary
by MITRE
An exploitable integer underflow vulnerability exists in the mdnscap binary of the CUJO Smart Firewall, version 7003. When parsing SRV records in an mDNS packet, the "RDLENGTH" value is handled incorrectly, leading to an out-of-bounds access that crashes the mdnscap process. An unauthenticated attacker can send an mDNS message to trigger this vulnerability.
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Analysis
by VulDB Data Team • 08/03/2023
The CVE-2018-4011 vulnerability represents a critical integer underflow flaw in the mdnscap binary component of the CUJO Smart Firewall firmware version 7003. This vulnerability resides within the multicast dns capture utility that processes mDNS packets, specifically when handling SRV record types. The flaw manifests during the parsing of network traffic where the RDLENGTH field in DNS resource records is improperly validated, creating a condition where arithmetic operations result in negative values that subsequently trigger memory access violations. The vulnerability impacts the firewall's ability to process legitimate network discovery traffic while simultaneously creating a potential denial of service vector. This issue falls under the CWE-191 category of Integer Underflow, which is classified as a fundamental weakness in the software's input validation mechanisms. The ATT&CK framework would categorize this under T1071.004 Application Layer Protocol: DNS, as it involves manipulation of DNS packet structures to exploit the underlying system.
The technical implementation of this vulnerability occurs when the mdnscap binary processes incoming mDNS packets containing SRV records. During parsing, the system reads the RDLENGTH field which indicates the length of the resource data field in bytes. When this value is manipulated to cause an integer underflow condition, the resulting negative value is used as an array index or memory allocation parameter. This leads to memory corruption and subsequent process termination when the system attempts to access memory locations outside the valid bounds of the allocated buffer. The vulnerability is particularly dangerous because it can be triggered by any unauthenticated attacker who can send specially crafted mDNS packets to the affected firewall. The integer underflow creates a scenario where the system's memory management routines are bypassed, leading to unpredictable behavior and process crashes that effectively disrupt the firewall's network monitoring capabilities.
The operational impact of CVE-2018-4011 extends beyond simple denial of service, as it represents a significant security risk for network infrastructure relying on CUJO firewalls. When exploited, the vulnerability can cause complete service disruption for network monitoring functions, leaving the protected network vulnerable to undetected attacks during the period when the mdnscap process is unavailable. The firewall's ability to perform network discovery and monitoring tasks becomes compromised, potentially allowing malicious actors to bypass security controls that depend on proper DNS resolution and service discovery. Organizations using affected firmware versions face increased risk of network infiltration, as the firewall's capacity to detect and respond to suspicious network activity is severely degraded. The vulnerability also demonstrates poor software security practices in the handling of network protocol parsing, indicating potential for similar flaws in other network services within the same firmware ecosystem.
Mitigation strategies for CVE-2018-4011 should focus on immediate firmware updates provided by the vendor, as this vulnerability requires core system modifications to address the integer underflow condition properly. Network administrators should implement network segmentation to limit exposure to potential attackers and monitor for unusual mDNS traffic patterns that might indicate exploitation attempts. The implementation of intrusion detection systems that can identify malformed mDNS packets should be considered as a temporary workaround while awaiting official patches. Additionally, organizations should conduct thorough network audits to identify all CUJO firewall instances and ensure proper patch management protocols are in place. Security teams should also review their incident response procedures to account for potential service disruption scenarios and establish protocols for rapid recovery when such vulnerabilities are exploited. The vulnerability underscores the importance of robust input validation and memory safety practices in network security appliances, particularly those handling real-time packet processing and network monitoring functions.