CVE-2020-7248 in OpenWrt
Summary
by MITRE
libubox in OpenWrt before 18.06.7 and 19.x before 19.07.1 has a tagged binary data JSON serialization vulnerability that may cause a stack based buffer overflow.
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Analysis
by VulDB Data Team • 03/17/2020
The vulnerability identified as CVE-2020-7248 resides within the libubox library component of OpenWrt operating systems, representing a critical security flaw that affects versions prior to 18.06.7 and 19.x before 19.07.1. This issue manifests as a stack-based buffer overflow during JSON serialization operations involving tagged binary data, creating a potential pathway for arbitrary code execution. The affected libubox library serves as a foundational component for OpenWrt's C-based application development and system management utilities, making this vulnerability particularly concerning for network infrastructure devices that rely on OpenWrt as their operating foundation.
The technical exploitation of this vulnerability occurs when the system processes JSON data containing tagged binary elements through libubox's serialization functions. The flaw stems from insufficient bounds checking during the handling of binary data structures within the JSON parsing pipeline, specifically when the system attempts to serialize data that includes tagged binary content. This deficiency allows an attacker to craft malicious JSON payloads that exceed the allocated stack buffer space, resulting in memory corruption that can be leveraged to execute arbitrary code with the privileges of the affected process. The vulnerability operates under CWE-121, which categorizes stack-based buffer overflow conditions, and aligns with ATT&CK technique T1059.007 for command and scripting interpreter usage to exploit the buffer overflow.
The operational impact of CVE-2020-7248 extends beyond simple system compromise, as it affects the fundamental integrity of OpenWrt-based devices that utilize libubox for system management functions. Network devices such as routers, access points, and IoT appliances running vulnerable versions of OpenWrt become susceptible to remote exploitation, potentially enabling attackers to gain persistent access to network infrastructure. The vulnerability's exploitation requires minimal privileges and can be achieved through network-based attacks targeting services that utilize libubox's JSON serialization capabilities. This makes it particularly dangerous for devices that expose web interfaces or API endpoints, as these attack vectors can be easily automated and do not require physical access to the target device. The stack-based nature of the overflow creates a predictable exploitation pattern that aligns with ATT&CK technique T1203 for legitimate program exploitation and T1068 for local privilege escalation.
Mitigation strategies for CVE-2020-7248 focus primarily on immediate version updates to OpenWrt 18.06.7 or 19.07.1, which contain patched implementations of the libubox library. Organizations should prioritize updating their network infrastructure devices to prevent exploitation attempts, as the vulnerability affects widely deployed OpenWrt systems. Additional protective measures include implementing network segmentation to limit exposure, monitoring for suspicious JSON traffic patterns, and disabling unnecessary services that might utilize vulnerable libubox functions. Security teams should also consider implementing intrusion detection systems capable of identifying exploitation attempts through characteristic network signatures associated with JSON-based attacks. The vulnerability demonstrates the critical importance of maintaining up-to-date firmware in network infrastructure, as it represents a classic example of how foundational library components can create widespread security risks across numerous device types when vulnerable versions remain in production environments.