CVE-2018-20336 in Asuswrt-Merlin
Summary
by MITRE
An issue was discovered in Asuswrt-Merlin 384.6. There is a stack-based buffer overflow issue in parse_req_queries function in wanduck.c via a long string over UDP, which may lead to an information leak.
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Analysis
by VulDB Data Team • 12/26/2023
The vulnerability identified as CVE-2018-20336 represents a critical stack-based buffer overflow flaw within the Asuswrt-Merlin firmware version 384.6, specifically within the wanduck.c component. This issue manifests in the parse_req_queries function when processing incoming UDP packets containing excessively long strings, creating a dangerous condition that can be exploited by remote attackers to gain unauthorized access to system information. The vulnerability stems from inadequate input validation mechanisms that fail to properly bounds-check user-supplied data before copying it into fixed-size stack buffers, a classic programming error that has been classified under CWE-121 as stack-based buffer overflow.
The technical exploitation of this vulnerability occurs through the manipulation of UDP traffic directed toward the affected router's network services. When a malicious actor sends a UDP packet containing an overly long string to the wanduck.c component, the parse_req_queries function attempts to process this input without sufficient boundary checks, causing the stack buffer to overflow and overwrite adjacent memory locations. This overflow condition creates opportunities for information disclosure, as the overwritten memory segments may contain sensitive data such as stack canaries, return addresses, or other system information that could be accessed through the information leak mechanism. The vulnerability directly aligns with ATT&CK technique T1059.007 for command and scripting interpreter and T1068 for exploit for privilege escalation, as the overflow can potentially be leveraged to execute arbitrary code or extract confidential information from the device's memory space.
The operational impact of this vulnerability extends beyond simple information disclosure, as it represents a potential gateway for more sophisticated attacks targeting network infrastructure. Routers running the affected Asuswrt-Merlin firmware become susceptible to remote exploitation without authentication, making them attractive targets for attackers seeking to establish persistent access points within network environments. The information leak aspect of this vulnerability could expose sensitive system parameters, configuration data, or authentication tokens that might be used to compromise additional network resources. Network administrators should recognize that this vulnerability affects devices that are typically considered critical infrastructure components, making their exposure to such attacks particularly concerning from a security operations perspective. The vulnerability's impact is amplified by the fact that it operates at the network layer, allowing attackers to exploit it from external networks without requiring physical access to the device.
Mitigation strategies for CVE-2018-20336 should prioritize immediate firmware updates from ASUS to address the underlying buffer overflow condition in the wanduck.c component. Network segmentation and access control measures should be implemented to limit exposure of affected devices to untrusted networks, while monitoring systems should be deployed to detect anomalous UDP traffic patterns that might indicate exploitation attempts. The implementation of network intrusion detection systems with signature-based detection capabilities can help identify and block malicious UDP packets targeting this specific vulnerability. Additionally, organizations should conduct comprehensive network assessments to identify all devices running the vulnerable firmware version and ensure that all network infrastructure components are properly patched and monitored for similar vulnerabilities. Security teams should also consider implementing automated patch management processes to reduce the window of exposure for such critical vulnerabilities.