CVE-2024-11253 Overview
CVE-2024-11253 is a post-authentication command injection vulnerability affecting the diagnostic function in multiple Zyxel customer-premises equipment (CPE) devices, including the VMG8825-T50K running firmware version V5.50(ABOM.8.5)C0 and earlier. The flaw resides in the handling of the DNSServer parameter, which fails to sanitize user-supplied input before passing it to an operating system shell. An authenticated attacker with administrator privileges can inject arbitrary OS commands and execute them on the underlying device. The vulnerability is tracked under CWE-78: Improper Neutralization of Special Elements used in an OS Command.
Critical Impact
Successful exploitation grants attackers full command execution on affected Zyxel DSL, Ethernet CPE, fiber ONT, and WiFi extender devices, enabling persistence, traffic interception, and lateral movement into subscriber networks.
Affected Products
- Zyxel VMG8825-T50K firmware V5.50(ABOM.8.5)C0 and earlier
- Zyxel VMG3927-T50K, VMG4005-B50A, VMG4005-B60A firmware
- Zyxel EMG5723-T50K and DM4200-B0 firmware
Discovery Timeline
- 2025-03-11 - Zyxel publishes the security advisory and releases fixed firmware
- 2025-03-11 - CVE-2024-11253 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2024-11253
Vulnerability Analysis
The vulnerability exists in the diagnostic function exposed through the device's administrative web interface. The DNSServer parameter, intended to accept an IP address for DNS diagnostic tests such as nslookup, is concatenated into a shell command string without adequate validation or escaping. When the diagnostic routine invokes the command, an attacker-supplied shell metacharacter breaks the intended command boundary and allows injection of additional commands.
Exploitation requires prior administrator authentication, reflected in the high privileges required to reach the vulnerable code path. Once authenticated, an attacker submits a crafted diagnostic request and the device executes the injected commands with the privileges of the diagnostic service, typically root. This enables firmware modification, credential harvesting, and pivoting to internal subscriber networks.
Root Cause
The root cause is improper neutralization of OS command elements (CWE-78) in the diagnostic handler. The affected firmware passes the DNSServer field directly into a system shell invocation, treating attacker-controlled input as trusted. Shell metacharacters such as ;, |, &&, and backticks retain their control meaning, letting an attacker append or chain commands.
Attack Vector
The attack vector is network-based against the device management interface. An authenticated administrator issues a diagnostic request containing shell metacharacters in the DNSServer field. The device processes the request server-side and runs the injected commands. When management interfaces are exposed to the WAN or reachable through weak or reused credentials, the practical barrier to exploitation is low.
See the Zyxel Security Advisory for vendor technical details.
Detection Methods for CVE-2024-11253
Indicators of Compromise
- Diagnostic HTTP POST requests to the device management interface containing shell metacharacters (;, |, `, $() in the DNSServer parameter.
- Unexpected outbound connections from the CPE device to unknown hosts following administrative logins.
- Modifications to device firmware, /etc configuration files, or persistent scheduled tasks not initiated by an operator.
Detection Strategies
- Inspect device HTTP access logs for diagnostic endpoint requests with abnormal DNSServer values that do not match a valid IPv4 or IPv6 address.
- Correlate administrator authentication events with subsequent diagnostic function usage to identify unusual sequences.
- Alert on new listening sockets, reverse shell processes, or unexpected DNS traffic sourced from managed CPE devices.
Monitoring Recommendations
- Forward device syslog and web management logs to a central SIEM for retention and correlation.
- Track failed and successful admin logins to CPE devices from WAN-facing IP addresses.
- Baseline typical firmware versions across the fleet and alert on unexpected changes.
How to Mitigate CVE-2024-11253
Immediate Actions Required
- Upgrade affected Zyxel VMG, EMG, and DM series devices to the fixed firmware listed in the vendor advisory.
- Rotate administrator credentials and disable any default or shared accounts on affected devices.
- Restrict management interface access to trusted internal networks only; disable WAN-side administration.
Patch Information
Zyxel released patched firmware for the affected DSL, Ethernet CPE, fiber ONT, and WiFi extender models on 2025-03-11. Refer to the Zyxel Security Advisory for the specific firmware versions that remediate CVE-2024-11253 across each affected model.
Workarounds
- Disable remote management on the WAN interface until the patched firmware is deployed.
- Enforce strong, unique administrator passwords and enable account lockout on repeated authentication failures.
- Place management traffic behind a VPN or jump host to reduce exposure of the diagnostic function.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
