CVE-2020-17444 in picoTCP
Summary
by MITRE • 12/12/2020
An issue was discovered in picoTCP 1.7.0. The routine for processing the next header field (and deducing whether the IPv6 extension headers are valid) doesn't check whether the header extension length field would overflow. Therefore, if it wraps around to zero, iterating through the extension headers will not increment the current data pointer. This leads to an infinite loop and Denial-of-Service in pico_ipv6_check_headers_sequence() in pico_ipv6.c.
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Analysis
by VulDB Data Team • 12/16/2020
The vulnerability identified as CVE-2020-17444 resides within picoTCP version 1.7.0, a lightweight TCP/IP stack implementation designed for embedded systems and resource-constrained environments. This flaw manifests in the IPv6 header processing functionality where the software fails to validate the integrity of extension header length fields during packet parsing operations. The issue specifically impacts the pico_ipv6_check_headers_sequence() function located in pico_ipv6.c, which serves as a critical component for verifying the correctness of IPv6 packet structures before further processing.
The technical root cause of this vulnerability stems from inadequate input validation within the IPv6 extension header processing routine. When the next header field contains a malformed length value that causes arithmetic overflow resulting in a zero value, the packet parsing logic becomes trapped in an infinite loop. This occurs because the data pointer tracking the current position within the packet payload fails to advance properly when the header length field wraps around to zero. The vulnerability represents a classic case of insufficient bounds checking and integer overflow handling, which directly maps to CWE-191 Integer Underflow (Wrap or Wraparound) and CWE-129 Improper Validation of Array Index.
The operational impact of this vulnerability is severe as it enables a remote attacker to trigger a Denial-of-Service condition against systems utilizing picoTCP 1.7.0. The infinite loop consumes excessive CPU resources and prevents the system from processing legitimate network traffic, effectively rendering the affected device or application non-responsive. This type of vulnerability is particularly dangerous in embedded systems, IoT devices, and network infrastructure where continuous operation is critical. The attack requires only sending a specially crafted IPv6 packet with malformed extension headers, making it accessible to attackers with minimal privileges and technical expertise. From an adversary perspective, this vulnerability aligns with ATT&CK technique T1499.004 Network Denial of Service, as it specifically targets network service availability through packet manipulation.
The mitigation strategy for CVE-2020-17444 involves implementing proper bounds checking and integer overflow validation within the IPv6 header processing routine. Developers should ensure that extension header length fields are validated against maximum allowable values before processing, preventing the wraparound condition that leads to the infinite loop. Additionally, implementing defensive programming practices such as explicit bounds checking, proper integer overflow detection, and robust error handling mechanisms will prevent similar vulnerabilities from occurring in future implementations. The fix should also include proper termination conditions for header iteration loops and validation of header field consistency to prevent malicious packet structures from causing system instability. Organizations using picoTCP should upgrade to version 1.7.1 or later where this vulnerability has been addressed through proper input validation and bounds checking mechanisms.