CVE-2026-25857: Tenda G300-F Router RCE Vulnerability

CVE-2026-25857 Overview

CVE-2026-25857 is a critical OS command injection vulnerability affecting the Tenda G300-F router firmware. The vulnerability exists in the WAN diagnostic functionality (formSetWanDiag), where the implementation constructs a shell command that invokes curl and incorporates attacker-controlled input into the command line without adequate neutralization. This allows a remote attacker with access to the affected management interface to inject additional shell syntax and execute arbitrary commands on the device with the privileges of the management process.

Critical Impact

Remote attackers can achieve complete device compromise through arbitrary command execution on affected Tenda G300-F routers, potentially leading to network infrastructure takeover.

Affected Products

• Tenda G300-F router firmware version 16.01.14.2
• Tenda G300-F router firmware versions prior to 16.01.14.2

Discovery Timeline

• 2026-02-07 - CVE CVE-2026-25857 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-25857

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 resides in the formSetWanDiag function within the Tenda G300-F router's web management interface.

The vulnerable implementation constructs shell commands dynamically by concatenating user-supplied input directly into command strings without proper sanitization or validation. When the router's WAN diagnostic functionality is invoked, it utilizes the curl command to perform network diagnostics. However, the parameters passed to this function are not adequately neutralized, allowing an attacker to inject arbitrary shell metacharacters and commands.

An authenticated attacker with access to the router's management interface can craft malicious input containing shell command separators (such as ;, |, &&, or backticks) to break out of the intended command context and execute arbitrary commands with the same privileges as the router's management process—typically root-level access on embedded devices.

Root Cause

The root cause of this vulnerability is insufficient input validation and improper neutralization of special shell characters in the formSetWanDiag function. The firmware fails to sanitize user-controllable parameters before incorporating them into dynamically constructed shell commands, violating secure coding practices for OS command handling.

Attack Vector

The attack is conducted over the network against the router's web management interface. An attacker requires authenticated access to the management interface to exploit this vulnerability. The attacker can inject shell metacharacters into the diagnostic parameters, causing the router to execute arbitrary commands. This could result in complete device compromise, persistent backdoor installation, network traffic interception, or use of the device as a pivot point for further attacks within the network.

For detailed technical analysis of the exploitation mechanism, refer to the security advisory from VulnCheck or the detailed CVE analysis on Evan's Blog.

Detection Methods for CVE-2026-25857

Indicators of Compromise

• Unexpected processes running on the router such as reverse shells, wget/curl downloads to unusual destinations, or persistent connections to external IP addresses
• Modified system files or configurations on the router that were not performed by authorized administrators
• Unusual outbound network connections originating from the router to unknown command-and-control infrastructure
• Log entries showing suspicious diagnostic function calls containing shell metacharacters (;, |, &&, `)

Detection Strategies

• Monitor HTTP traffic to the router's management interface for requests to the formSetWanDiag endpoint containing shell metacharacters or command injection patterns
• Implement network-based intrusion detection rules to identify command injection attempts targeting Tenda router management interfaces
• Deploy SentinelOne Singularity for IoT/Network to detect anomalous behavior from network infrastructure devices
• Review router access logs for authentication events followed by suspicious diagnostic function invocations

Monitoring Recommendations

• Enable comprehensive logging on network segments where Tenda routers are deployed
• Implement alerting for any management interface access from untrusted networks or IP addresses
• Regularly audit running processes and network connections on affected devices if shell access is available
• Monitor for firmware integrity changes or unauthorized configuration modifications

How to Mitigate CVE-2026-25857

Immediate Actions Required

• Restrict access to the router's management interface to trusted administrative networks only using firewall rules or VLANs
• Disable remote management access from WAN interfaces if not strictly required
• Implement strong authentication credentials and change default passwords on all affected devices
• Consider network segmentation to isolate affected routers from critical systems until patching is available

Patch Information

At the time of publication, check the Tenda Material Download page for updated firmware versions that address this vulnerability. Organizations should apply the latest firmware update as soon as it becomes available from the vendor.

Workarounds

• Restrict management interface access to localhost or trusted administrator IP addresses only
• Place affected routers behind additional firewall protection that filters malicious input patterns
• If the WAN diagnostic feature is not required, consider disabling it through available configuration options
• Implement network access controls to prevent unauthorized users from reaching the management interface

# Example: Restrict management access via iptables on upstream firewall
# Allow management interface access only from trusted admin subnet
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP