CVE-2023-24479: TALOS-2023-1762 || Cisco Talos Intelligence Group

SUMMARY

An authentication bypass vulnerability exists in the httpd nvram.cgi functionality of Yifan YF325 v1.0_20221108. A specially crafted network request can lead to arbitrary command execution. An attacker can send a network request to trigger this vulnerability.

CONFIRMED VULNERABLE VERSIONS

The versions below were either tested or verified to be vulnerable by Talos or confirmed to be vulnerable by the vendor.

Yifan YF325 v1.0_20221108

PRODUCT URLS

YF325 - https://yifanwireless.com/entry-level-wifi-router/yf325-series-gprs/3g/4g-wifi-router-with-sim-card-slot.html

CVSSv3 SCORE

9.8 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE

CWE-284 - Improper Access Control

DETAILS

The Yifan YF325 is an industrial cellular router. This device is designed for M2M and IOT applications, allowing remote management, offering several VPN services and many other features.

The YF325 router provides a series of APIs. The API that manages the nvram.cgi* endpoints uses the httpd’s parse_nvram_file function to manage the incoming data:

void parse_nvram_file(undefined4 param_1,int fd,size_t content_length)
  {
    [...]
    do {
      if ((int)content_length < 1) break;
      read_size = 0x400;
      if (content_length + 1 < 0x401) {
        read_size = content_length + 1;
      }
      read_bytes = wfgets(temp_buf,read_size,fd);
      if (read_bytes == 0) {
        return;
      }
      current_len = strlen(temp_buf);
      content_length = content_length - current_len;
      is_equal = strncasecmp(temp_buf,"Content-Disposition:",0x14);
    } while ((is_equal != 0) || (pcVar3 = strstr(temp_buf,"name=\"file\""), pcVar3 == (char *)0x0));
    while (0 < (int)content_length) {
      read_bytes = wfgets(temp_buf,0x400,fd);
      if (read_bytes == 0) {
        return;
      }
      current_len = strlen(temp_buf);
      content_length = content_length - current_len;
      is_equal = strcmp(temp_buf,"\n");
      if ((is_equal == 0) || (is_equal = strcmp(temp_buf,"\r\n"), is_equal == 0)) break;
    }
    [...]
    restore_fd = fopen("/tmp/restore.bin","wb");
    [... read the request's uploaded file and write it into the "/tmp/restore.bin" file ...]
    res = nvram_restore("/tmp/restore.bin");
    [...]
    return;
  }

The nvram_restore function will open the file specified by the first argument, parse it and commit the new nvram variables. Because this function is reachable prior to authentication, this is a vulnerability. Indeed, an attacker could change the admin credentials of the device and obtain root access.

TIMELINE

2023-06-28 - Initial Vendor Contact
2023-07-06 - Vendor Disclosure
2023-10-11 - Public Release

Discovered by Francesco Benvenuto of Cisco Talos.