CVE-2025-34117 Overview
A critical remote code execution vulnerability exists in multiple Netcore and Netis router models with firmware released prior to August 2014. The vulnerability stems from the presence of an undocumented backdoor listener on UDP port 53413 that allows unauthenticated remote attackers to execute arbitrary commands on affected devices.
The backdoor uses a hardcoded authentication mechanism and accepts shell commands post-authentication, effectively bypassing all router security controls. This firmware-level vulnerability represents a severe supply chain security issue, as the backdoor was intentionally embedded in the router firmware. Some device models include a non-standard implementation of the echo command, which may affect exploitability.
Critical Impact
Unauthenticated remote attackers can gain complete control of affected routers by sending specially crafted UDP packets to port 53413, enabling network traffic interception, lateral movement, and persistent access to internal networks.
Affected Products
- Netcore routers with firmware released prior to August 2014
- Netis routers with firmware released prior to August 2014
- Exact model and version boundaries remain undocumented by the vendor
Discovery Timeline
- 2025-07-16 - CVE-2025-34117 published to NVD
- 2025-07-17 - Last updated in NVD database
Technical Details for CVE-2025-34117
Vulnerability Analysis
This vulnerability is classified as CWE-78 (Improper Neutralization of Special Elements used in an OS Command), commonly known as OS Command Injection. The flaw exists because the affected routers contain an intentionally embedded backdoor service that listens on UDP port 53413 on the WAN interface.
When an attacker sends a specially crafted UDP packet to this port, the router's firmware processes the request through a hardcoded authentication check. Upon successful authentication using known credentials, the backdoor grants shell access to the attacker, allowing execution of arbitrary system commands with root privileges on the underlying Linux-based router operating system.
The network-accessible nature of this vulnerability, combined with no authentication requirements for initial access and low attack complexity, makes exploitation trivial for remote attackers. The vulnerability has an EPSS score of 50.3% (97.81st percentile), indicating a high probability of active exploitation.
Root Cause
The root cause is an intentionally embedded backdoor listener in the router firmware that binds to UDP port 53413 on all network interfaces, including the WAN-facing interface. This backdoor was apparently included during the manufacturing process and uses a hardcoded authentication mechanism that cannot be disabled or modified by end users. The service accepts shell commands after authentication, providing direct command execution capabilities without any access controls or logging.
Attack Vector
The attack vector is network-based, requiring the attacker to have network visibility to UDP port 53413 on the target router's WAN interface. Exploitation involves sending crafted UDP packets containing authentication credentials followed by shell commands.
The attack flow typically follows these steps:
- Attacker scans for vulnerable routers by probing UDP port 53413
- Upon receiving a response indicating an active backdoor, the attacker sends authentication credentials
- After successful authentication, the attacker sends arbitrary shell commands
- Commands execute with root privileges on the router's embedded Linux system
A Metasploit module (netcore_udp_53413_backdoor) is publicly available that automates this exploitation process, as documented in the Metasploit Framework repository. Additional exploit code is available via Exploit-DB #43387.
Detection Methods for CVE-2025-34117
Indicators of Compromise
- Unexpected UDP traffic to or from port 53413 on router interfaces
- Outbound connections from router management interface to unknown external IP addresses
- Unauthorized DNS configuration changes or traffic redirection
- Modified router firmware or configuration files
Detection Strategies
- Configure network monitoring to alert on any UDP traffic to/from port 53413
- Deploy intrusion detection system (IDS) rules to detect known exploitation patterns targeting Netcore/Netis backdoor
- Monitor for Metasploit signature patterns associated with netcore_udp_53413_backdoor module
- Implement network segmentation to isolate potentially affected legacy routers
Monitoring Recommendations
- Enable logging on perimeter firewalls to capture UDP port 53413 activity
- Subscribe to threat intelligence feeds that track vulnerable Netcore/Netis router activity, such as the Shadowserver vulnerability scan reports
- Periodically audit network infrastructure for legacy or end-of-life router equipment
- Monitor router configurations for unauthorized changes to DNS servers, routing tables, or firewall rules
How to Mitigate CVE-2025-34117
Immediate Actions Required
- Block UDP port 53413 inbound and outbound at the network perimeter firewall immediately
- Identify and inventory all Netcore and Netis router devices in the environment
- Isolate affected routers from production networks until remediation is complete
- Replace affected routers with supported hardware from vendors with strong security track records
Patch Information
No official vendor patch is available for this vulnerability. The affected firmware was released prior to August 2014, and exact version boundaries remain undocumented by the vendor. Organizations should treat this as an end-of-life vulnerability requiring hardware replacement rather than patching.
For additional technical details, refer to the VulnCheck Security Advisory and Trend Micro's technical analysis.
Workarounds
- Block UDP port 53413 at all network boundaries using firewall rules
- If the router supports it, configure access control lists (ACLs) to prevent external access to the management interface
- Place affected routers behind a separate firewall that blocks port 53413 traffic
- Implement network segmentation to minimize the impact of a compromised router
# Firewall rule example (iptables) to block backdoor port
iptables -A INPUT -p udp --dport 53413 -j DROP
iptables -A OUTPUT -p udp --sport 53413 -j DROP
iptables -A FORWARD -p udp --dport 53413 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
