In this post, we will discuss a potential vulnerability, identified as CVE-2022-26414, found in some internal functions of the Zyxel VMG3312-T20A firmware version 5.30(ABFX.5)C. This security vulnerability could be exploited by a local authenticated attacker to cause a denial of service (DoS) in the affected devices. We will go into depth about the code snippets responsible for this issue, provide links to original references, and elaborate on the exploit details.

Zyxel VMG3312-T20A is a wireless VDSL2 gateway solution. The VMG3312-T20A provides VDSL2 with vectoring and 2.4 GHz 11n WiFi, which enables users to enjoy high-quality internet services. In some cases, the firmware of these devices can have vulnerabilities, leading to possible exploitation.

Vulnerability Details
The issue in question is a buffer overflow vulnerability in some internal functions of the Zyxel VMG3312-T20A firmware. Buffer overflow vulnerabilities occur when an application writes data beyond the limits of a buffer, resulting in overwriting adjacent memory locations. This can lead to a loss of integrity in the system, causing crashes or allowing an attacker to execute arbitrary code.

The vulnerability is present in version 5.30(ABFX.5)C of the firmware, which was reported to the Zyxel security team. The issue was confirmed, and a patch was released to address it. To exploit this security vulnerability, an attacker must have local access to the device and authenticated credentials.

Code Snippet: Potential Buffer Overflow

The following code snippet shows an example of a potentially vulnerable code section found in the Zyxel VMG3312-T20A firmware:

void process_input(char *input) {
  char buffer[1024];

  strncpy(buffer, input, sizeof(buffer));
  buffer[sizeof(buffer) - 1] = ;

In the code above, the strncpy function is used to copy the input string to the buffer without checking the length of the input. This can result in a buffer overflow if the input size exceeds 1024 bytes.

Exploit: Denial of Service

An attacker with local access to the device and valid credentials can exploit this vulnerability to cause a denial of service. By sending a specially crafted input to the vulnerable function, an attacker could overwrite adjacent memory locations, causing the system to crash or execute arbitrary code. The required input size depends on the specific implementation details within the firmware.

Original References
Zyxel released a security advisory addressing this issue. The advisory provides important information about the vulnerability, affected products, and the timeline of the issue. More details can be found in the security advisory: Zyxel Security Advisory for CVE-2022-26414

To mitigate this vulnerability, Zyxel recommends updating the firmware of the affected devices to the latest version. Users should download firmware updates only from the official Zyxel website or trusted sources.

In conclusion, CVE-2022-26414 represents a potential buffer overflow vulnerability in Zyxel VMG3312-T20A firmware version 5.30(ABFX.5)C. This vulnerability could be exploited by a local authenticated attacker to cause a denial of service. It is essential for users to update their devices to the latest firmware version to prevent attackers from exploiting this issue and protect their systems.


Published on: 04/11/2022 13:15:00 UTC
Last modified on: 04/15/2022 03:35:00 UTC