CVE-2020-17441 in picoTCP
Summary
by MITRE • 12/12/2020
An issue was discovered in picoTCP 1.7.0. The code for processing the IPv6 headers does not validate whether the IPv6 payload length field is equal to the actual size of the payload, which leads to an Out-of-Bounds read during the ICMPv6 checksum calculation, resulting in either Denial-of-Service or Information Disclosure. This affects pico_ipv6_extension_headers and pico_checksum_adder (in pico_ipv6.c and pico_frame.c).
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Analysis
by VulDB Data Team • 12/16/2020
The vulnerability CVE-2020-17441 resides within picoTCP version 1.7.0, a lightweight TCP/IP stack designed for embedded systems and IoT devices. This issue stems from inadequate validation of IPv6 header fields during packet processing, specifically targeting the payload length field that governs the size of the IPv6 payload. The flaw exists in the core IPv6 processing functions where the system fails to verify that the declared payload length matches the actual data size being processed, creating a fundamental mismatch between expected and actual packet dimensions.
The technical implementation of this vulnerability occurs within the pico_ipv6_extension_headers and pico_checksum_adder functions located in pico_ipv6.c and pico_frame.c files. When an IPv6 packet arrives with a malformed payload length field, the system proceeds to calculate ICMPv6 checksums without proper bounds checking. This leads to an out-of-bounds read condition where the checksum calculation routine attempts to access memory locations beyond the allocated payload buffer. The absence of proper validation allows attackers to craft malicious IPv6 packets that manipulate the payload length field to point beyond the actual packet boundaries, triggering memory access violations.
The operational impact of this vulnerability manifests as either denial-of-service or information disclosure depending on the specific memory access pattern triggered by the out-of-bounds read. In denial-of-service scenarios, the system may crash or become unresponsive due to memory access violations, rendering the network stack inoperative and disrupting network connectivity for affected devices. When information disclosure occurs, the out-of-bounds read may expose sensitive data from adjacent memory regions, potentially including cryptographic keys, session information, or other confidential data stored in memory. This vulnerability affects embedded systems and network appliances that rely on picoTCP for IPv6 communication, particularly those deployed in critical infrastructure where continuous operation is essential.
This vulnerability aligns with CWE-129, which addresses improper validation of array index bounds, and CWE-125, which covers out-of-bounds read conditions. The attack pattern follows techniques described in the MITRE ATT&CK framework under T1059 for command and control through network protocols, and T1499 for network denial of service. The flaw represents a classic buffer over-read vulnerability that exploits the lack of input validation in network protocol processing, making it particularly dangerous in embedded environments where system resources are limited and recovery mechanisms may be insufficient. Organizations using picoTCP in production environments should prioritize immediate patching and implement network segmentation to limit the potential impact of exploitation attempts.
The root cause of this vulnerability demonstrates a fundamental flaw in defensive programming practices where input validation is insufficiently applied to critical network protocol fields. The lack of bounds checking in the IPv6 payload length verification creates a pathway for attackers to manipulate packet processing flows, potentially leading to cascading failures in networked embedded systems. This vulnerability underscores the importance of rigorous input validation in network protocol implementations and highlights the need for comprehensive testing of edge cases in packet processing routines, particularly in embedded systems where resource constraints may limit the effectiveness of traditional security mitigations.