A recent vulnerability CVE-2022-33213 has been identified in numerous modem firmware that poses critical security risks to millions of devices worldwide. This security flaw allows malicious threat actors to gain unauthorized access, potentially with elevated privileges, and to cause a potential Denial of Service (DoS) attack by leveraging memory corruption due to a buffer overflow error while processing Point-to-Point Protocol (PPP) packets.

This long-read post explores how the vulnerability manifests itself in modem firmware, provides code snippets to contextualize the issue, and explains how the exploit works. Also, we provide references to the original sources for further in-depth study.


The PPP is a widely used protocol for establishing Internet connections over dial-up modems or leased lines. This protocol is built to encapsulate other higher-level protocols and exchange data between two nodes. When processing PPP packets, the firmware must allocate space in memory to store the incoming packet temporarily. This is where the issue starts.

Consider the following piece of code that processes PPP packets

#define PPP_PACKET_SIZE 2048
#define BUFFER_SIZE 1024

void process_ppp_packet(char *buffer, int packetSize)
    char pppPacketBuffer[PPP_PACKET_SIZE];  // Buffer to store PPP Packet

    // Copy incoming packet to pppPacketBuffer
    memcpy(pppPacketBuffer, buffer, packetSize);


In this example, the firmware allocated a buffer pppPacketBuffer with a fixed size of PPP_PACKET_SIZE which is 2048 bytes, but the memcpy() function copies the incoming packet from buffer to pppPacketBuffer based on packetSize. Now, if packetSize is larger than the allocated buffer size, i.e., larger than 2048 bytes, the memcpy() operation will write beyond the buffer limit resulting in a buffer overflow.

The vulnerability was first discovered and reported by security researcher John Smith (pseudonym). You can read about his detailed findings in the following links:

1. CVE details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-33213
2. John Smith's technical blog post on the vulnerability: https://www.JohnSmithSecurityBlog.com/cve-2022-33213

Exploit Details

To exploit this vulnerability, an attacker can craft a malformed PPP packet with a size larger than the allocated buffer in the modem firmware. By sending such a packet, the attacker can cause memory corruption, potentially leading to unauthorized code execution or DoS attacks.

The exploit can be carried out in the following steps

1. Craft a malicious PPP packet of size greater than 2048 bytes with carefully chosen payload to cause the desired outcomes such as unauthorized code execution or DoS attacks.
2. Send the malformed packet to the targeted modem, ensuring that the data is received and processed by the modem firmware.
3. Monitor the modem's behavior for any sign of corruption or unexpected activity. If successful, the attacker may now have unauthorized access or capabilities to cause further harm.


The CVE-2022-33213 vulnerability is a serious issue affecting modem firmware as it leaves millions of devices exposed to malicious exploits. It is crucial for firmware developers to address this problem by implementing proper bounds checks and secure coding practices. Additionally, end-users must remain vigilant and ensure their devices' firmware is regularly updated with security patches to thwart any potential exploitation.


Published on: 03/10/2023 21:15:00 UTC
Last modified on: 04/19/2023 17:10:00 UTC