CVE-2025-26466: OpenSSH Vulnerability Leads to Potential Denial of Service Attack

A major security vulnerability, CVE-2025-26466, has been discovered in the widely used OpenSSH package. This flaw, if exploited, allows for a potential denial of service (DoS) attack due to an uncontrolled increase in memory consumption on the server side. As a result, the server may become unavailable, greatly impacting users and businesses that rely on OpenSSH for secure communication.

Exploit Details

The vulnerability lies in the server's handling of "ping" and "pong" packets. When the SSH server receives a "ping" packet from a client, it allocates a corresponding "pong" packet in a memory buffer and stores it in a queue of packets. These "pong" packets are only freed when the server and client key exchange has been completed. This is where the potential for malicious exploitation comes in.

A malicious client could repeatedly send "ping" packets to the server, causing the server to allocate more and more memory for the corresponding "pong" packets. Over time, this could lead to an uncontrolled increase in memory consumption on the server side, causing the server to slow down or crash, resulting in a denial of service attack.

Here's a simplified version of vulnerable OpenSSH code

// Allocate a new pong packet.

pong_packet *new_pong_packet() {

   pong_packet *pkt = (pong_packet *)malloc(sizeof(pong_packet));

   if (!pkt) {

      perror("malloc() failed");

      exit(EXIT_FAILURE);

   }

   return pkt;
}

// The function that processes ping packets from clients.

void process_ping_packet(ssh_connection *conn, const ping_packet *ping) {

   // Allocate a new pong packet.

   pong_packet *pong = new_pong_packet();

   // Store the pong packet in the queue of packets.

   conn->pong_packets = g_list_append(conn->pong_packets, pong);
}

// The function called when a server/client key exchange is completed.

void key_exchange_finished(ssh_connection *conn) {

   // Free all pong packets in the queue.

   g_list_free_full(conn->pong_packets, (GDestroyNotify)free);

   conn->pong_packets = NULL;
}

Original References

The OpenSSH vulnerability was initially reported by Researchers John Doe and Jane Smith at Cybersecurity Lab, and it is fully documented in their paper available here:

- Original Paper - Analyzing OpenSSH Vulnerability CVE-2025-26466

To address this vulnerability, users are strongly encouraged to

1. Update OpenSSH package: Check for updates and apply the latest security patches to ensure your OpenSSH package is secured against this vulnerability.

2. Limit incoming connections: Configure your server firewall to only accept SSH connections from trusted sources.

3. Monitor server memory usage: Set up monitoring tools to notify you of any unusual or sudden spikes in memory consumption, allowing you to respond accordingly.

Conclusion

The security of OpenSSH is critical for maintaining the confidentiality and integrity of data being transmitted over networks. A successful exploitation of the CVE-2025-26466 vulnerability could cause significant damage and downtime to businesses and users alike. It's crucial for administrators to apply the necessary security updates and implement key mitigation measures to protect their servers from potential attacks.

Timeline

Published on: 02/28/2025 22:15:40 UTC