CVE-2020-17437 in uIP
Summary
by MITRE • 12/12/2020
An issue was discovered in uIP 1.0, as used in Contiki 3.0 and other products. When the Urgent flag is set in a TCP packet, and the stack is configured to ignore the urgent data, the stack attempts to use the value of the Urgent pointer bytes to separate the Urgent data from the normal data, by calculating the offset at which the normal data should be present in the global buffer. However, the length of this offset is not checked; therefore, for large values of the Urgent pointer bytes, the data pointer can point to memory that is way beyond the data buffer in uip_process in uip.c.
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Analysis
by VulDB Data Team • 12/16/2020
The vulnerability described in CVE-2020-17437 represents a critical buffer overflow condition within the uIP TCP/IP stack implementation that affects Contiki 3.0 and related systems. This issue stems from inadequate input validation when processing TCP packets with the urgent flag set, creating a scenario where maliciously crafted network traffic can cause arbitrary memory access violations. The vulnerability exists specifically within the uip_process function in uip.c where the stack attempts to separate urgent data from normal data in the global buffer. When the stack is configured to ignore urgent data, it still processes the urgent pointer bytes to determine data offsets, but fails to validate the length of this calculated offset value.
The technical flaw manifests when the urgent pointer value exceeds the bounds of the allocated buffer space, allowing the data pointer to reference memory locations far beyond the intended buffer boundaries. This condition creates a classic buffer overflow scenario where the stack's memory management becomes compromised, potentially enabling attackers to overwrite adjacent memory regions or cause unexpected behavior in the network stack. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, where insufficient bounds checking allows memory access beyond allocated buffer limits. The implementation flaw occurs in the TCP packet processing logic where the stack assumes the urgent pointer value will always be within acceptable parameters without performing necessary validation checks.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it creates potential pathways for arbitrary code execution or information disclosure within affected systems. Systems running Contiki 3.0 or other products utilizing the vulnerable uIP stack become susceptible to remote exploitation when processing TCP packets with maliciously crafted urgent pointer values. Attackers can leverage this vulnerability to cause system crashes, potentially leading to persistent denial of service conditions, or in more sophisticated attacks, to execute arbitrary code within the context of the network stack process. The vulnerability affects embedded systems and IoT devices that rely on Contiki's lightweight TCP/IP stack implementation, making it particularly concerning for network infrastructure and connected devices where system stability is paramount.
Mitigation strategies for CVE-2020-17437 require immediate implementation of input validation measures within the TCP packet processing logic. System administrators should prioritize updating to patched versions of Contiki or applying the relevant security patches that implement proper bounds checking for urgent pointer values. The fix should ensure that all offset calculations are validated against buffer boundaries before any memory access operations are performed, preventing the data pointer from referencing memory locations outside the intended buffer space. Additionally, network administrators should consider implementing TCP packet filtering rules that can identify and drop packets with suspicious urgent pointer values, providing an additional layer of protection. This vulnerability demonstrates the importance of robust input validation in network stack implementations and aligns with ATT&CK technique T1071.004 for application layer protocol manipulation, where network protocol handling flaws are exploited to gain unauthorized access or cause system compromise.