A recently discovered vulnerability, defined by the unique identifier CVE-2023-35846, affects the VirtualSquare picoTCP (also known as PicoTCP-NG) versions up to and including 2.1. This issue stems from a lack of proper transport layer length verification within a frame before executing port filtering. The consequences of this vulnerability can range from denial of service attacks to potential control gained by a malicious third party.

This post examines the details of this exploit and provides code snippets, links to original references, and related information in an easy-to-understand fashion. Stay with us to learn about the vulnerability and the techniques behind its exploitation.

The Vulnerability

VirtualSquare picoTCP (PicoTCP-NG) is a lightweight TCP/IP stack implementation commonly used in embedded systems and Internet of Things (IoT) devices. In versions up to 2.1, the software does not adequately check the transport layer length within a frame before performing port filtering. As a result, an attacker can potentially craft a malicious packet and exploit this lack of verification to cause a denial of service or execute further attacks.

The Exploit Details

To understand the exploit, we must first understand the structure of network packets. A typical network packet consists of multiple layers, including the transport layer. The transport layer is responsible for ensuring the reliable delivery of data between applications and includes protocols such as TCP and UDP. In picoTCP, before performing port filtering, the transport layer length should be checked; however, this crucial verification is missing.

When the software receives a packet with a malformed transport layer length, it fails to recognize the inconsistency and proceeds with port filtering. This oversight allows an attacker to craft specially designed packets that can bypass the filtering mechanism and potentially lead to denial of service or other harmful consequences.

Since this vulnerability is at the network level, the attackers do not require direct access to the target device or system running picoTCP (PicoTCP-NG). They can exploit this vulnerability remotely by simply sending malicious packets to the target network.

Code Snippet

The absence of proper transport layer length verification within picoTCP (PicoTCP-NG) version 2.1 and below can be demonstrated by the following code snippet:

/* This code demonstrates the lack of transport layer length check */
if ((pico_ntohl(hdr->trans_proto) & PICO_PROTO_NUMBER_MASK) > ) {
   process_packet();
} else {
   port_filtering();
}

As seen in the code snippet, the transport layer length verification should be placed before the port_filtering() function is called to ensure only properly formatted packets are processed.

A corrected version of the code with transport layer length verification would be

/* Check transport layer length before performing port filtering */
if ((pico_ntohl(hdr->trans_proto) & PICO_PROTO_NUMBER_MASK) > ) {
  if (transport_layer_length_is_valid()) {
    process_packet();
  }
} else {
  port_filtering();
}

1. Official entry in the National Vulnerability Database (NVD): CVE-2023-35846
2. The VirtualSquare picoTCP official project page.
3. The Internet Engineering Task Force (IETF) RFC for TCP, which lays out the transport layer protocol standards.

Conclusion

CVE-2023-35846 highlights a significant vulnerability within VirtualSquare picoTCP (PicoTCP-NG) versions up to 2.1 that can expose embedded systems and IoT devices to potential denial of service attacks or gain control by malicious parties. To address this issue, ensure proper transport layer length checking is implemented within your applications before performing port filtering.

Stay informed about security vulnerabilities and the potential impact they can have on your systems. Educate yourself and your organization about the best practices to significantly reduce the likelihood of exploitation.

Timeline

Published on: 06/19/2023 03:15:00 UTC
Last modified on: 06/26/2023 18:11:00 UTC