CVE-2020-17443 in picoTCP
Summary
by MITRE • 12/12/2020
An issue was discovered in picoTCP 1.7.0. The code for creating an ICMPv6 echo replies doesn't check whether the ICMPv6 echo request packet's size is shorter than 8 bytes. If the size of the incoming ICMPv6 request packet is shorter than this, the operation that calculates the size of the ICMPv6 echo replies has an integer wrap around, leading to memory corruption and, eventually, Denial-of-Service in pico_icmp6_send_echoreply_not_frag in pico_icmp6.c.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 12/16/2020
The vulnerability CVE-2020-17443 resides within picoTCP version 1.7.0, a lightweight TCP/IP stack implementation commonly used in embedded systems and IoT devices. This issue represents a classic buffer overflow condition that stems from inadequate input validation in the ICMPv6 protocol handling mechanism. The flaw specifically manifests in the pico_icmp6_send_echoreply_not_frag function within pico_icmp6.c, where the system fails to properly validate the length of incoming ICMPv6 echo request packets before processing them.
The technical root cause of this vulnerability can be categorized as a CWE-129 input validation error, where the system does not properly check that the input data meets expected size constraints before proceeding with operations that depend on that data. When an ICMPv6 echo request packet arrives with a length shorter than the expected minimum of 8 bytes, the code performs arithmetic operations that result in integer wraparound behavior. This integer overflow condition occurs because the system attempts to calculate the size of the response packet based on the malformed input, leading to a situation where the calculated size becomes negative or exceeds the bounds of the allocated memory space.
The operational impact of this vulnerability extends beyond simple denial-of-service conditions to potentially enable more severe memory corruption scenarios. When the integer wraparound occurs during the calculation of the ICMPv6 echo reply size, it can cause the system to write data beyond the intended memory boundaries, resulting in unpredictable behavior that may include system crashes, memory corruption, or even potential code execution exploits. This vulnerability is particularly concerning in embedded environments where picoTCP is commonly deployed, as these systems often lack robust memory protection mechanisms that might otherwise prevent such corruption from escalating.
From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1499.004 for network denial-of-service attacks and represents a specific implementation flaw that could be exploited by attackers to disrupt network services. The vulnerability's exploitation requires minimal network access and can be achieved through sending specially crafted ICMPv6 echo request packets with malformed sizes. The low complexity of exploitation combined with the potential for system disruption makes this a significant concern for network infrastructure that relies on picoTCP implementations. Organizations should consider this vulnerability in their risk assessments, particularly when evaluating the security posture of IoT devices, embedded systems, and network appliances that utilize this TCP/IP stack implementation.
The fix for this vulnerability requires implementing proper input validation checks before any size calculations are performed on ICMPv6 echo request packets. The system must verify that incoming packets meet minimum size requirements and reject packets that are shorter than the expected 8-byte header size. Additionally, developers should implement bounds checking and integer overflow protection mechanisms to prevent the wraparound conditions that lead to memory corruption. This remediation approach addresses the underlying CWE-129 issue while ensuring that the ICMPv6 processing logic properly handles all valid input scenarios without exposing the system to memory corruption vulnerabilities that could lead to denial-of-service conditions or more severe exploitation outcomes.