CVE-2026-71916 Overview
CVE-2026-71916 is a command injection vulnerability affecting multiple DrayTek VigorSwitch models. The flaw resides in the commandTable function within the web management interface. Incomplete filtering of dangerous characters, including backticks, newline characters, and single quotes in the parameter field, allows attackers to inject arbitrary operating system commands. A remote attacker with valid administrative credentials can execute commands with root privileges on the affected device. The vulnerability is tracked under CWE-78, Improper Neutralization of Special Elements used in an OS Command.
Critical Impact
Authenticated remote attackers can execute arbitrary commands as root on affected DrayTek VigorSwitch devices, resulting in full device compromise.
Affected Products
- Multiple DrayTek VigorSwitch series models (see vendor advisory for specific model list)
- DrayTek VigorSwitch web management interface with the commandTable function
- Firmware versions prior to the August 2026 security fixes
Discovery Timeline
- 2026-08-24 - CVE-2026-71916 published to NVD
- 2026-08-27 - Last updated in NVD database
Technical Details for CVE-2026-71916
Vulnerability Analysis
The vulnerability exists in the commandTable function exposed through the VigorSwitch web management interface. The function accepts user-supplied input via the parameter field but performs incomplete sanitization of shell metacharacters. Backticks, newline characters, and single quotes are not filtered, allowing them to break out of the intended command context.
When crafted input reaches the underlying shell invocation, attacker-controlled data is interpreted as command syntax rather than a data value. The injected commands execute in the same process context as the web management service, which runs as root on VigorSwitch devices.
Successful exploitation grants attackers full control of the switch operating system, including the ability to modify configuration, pivot to adjacent networks, install persistent implants, or disrupt traffic. Exploitation requires valid administrative credentials, which limits opportunistic attacks but does not prevent post-compromise abuse or attacks by malicious insiders.
Root Cause
The root cause is improper neutralization of special elements in an OS command [CWE-78]. The commandTable function passes attacker-controlled parameter data to a shell interpreter without escaping backticks, newlines, or single quotes. Any of these characters can terminate the intended command and append attacker-defined commands to the execution stream.
Attack Vector
The attack vector is network-based against the switch's web management interface. An authenticated administrator sends a crafted HTTP request to the vulnerable endpoint containing shell metacharacters in the parameter field. The malicious payload triggers command execution as root on the device. Refer to the DrayTek Security Advisory August 2026 and the VulnCheck DrayTek OS Command Injection Advisory for technical exploitation details.
Detection Methods for CVE-2026-71916
Indicators of Compromise
- Unexpected HTTP POST requests to commandTable endpoints containing backticks, newline characters (%0a), or single quotes in the parameter field
- New or unrecognized processes spawned by the VigorSwitch web management service
- Outbound connections from the switch to unknown external hosts, indicating potential reverse shells or data exfiltration
- Unauthorized modifications to switch configuration, user accounts, or firmware
Detection Strategies
- Inspect HTTP traffic to the VigorSwitch web management interface for shell metacharacters in POST parameters, especially the parameter field
- Correlate administrative logins with subsequent anomalous outbound connections from the device
- Monitor for command-line indicators such as wget, curl, nc, or /bin/sh invocations sourced from the web service process
Monitoring Recommendations
- Enable and forward switch syslog and administrative audit logs to a central SIEM for correlation
- Alert on any web management interface authentication from IP addresses outside approved administrative ranges
- Baseline normal management traffic volume and content, then alert on deviations involving special characters
How to Mitigate CVE-2026-71916
Immediate Actions Required
- Apply the firmware update referenced in the DrayTek Security Advisory August 2026 as soon as it is available for your model
- Restrict web management interface access to a dedicated management VLAN or trusted administrative subnets only
- Rotate administrative credentials on all VigorSwitch devices and remove unused accounts
- Audit recent administrative logins and command history for signs of prior exploitation
Patch Information
DrayTek has published fixed firmware versions in the August 2026 security advisory. Consult the vendor advisory linked above for the specific fixed firmware version applicable to each VigorSwitch model. Deploy the patched firmware following DrayTek's standard update procedure and verify the running version after reboot.
Workarounds
- Disable remote access to the web management interface and restrict it to on-premises administrative hosts
- Enforce strong, unique administrative passwords and enable account lockout policies
- Place management interfaces behind a firewall or VPN, blocking direct exposure to untrusted networks
- Continuously monitor management-plane traffic for injection attempts until patches are deployed
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
