CVE-2026-71904 Overview
CVE-2026-71904 is an operating system command injection vulnerability [CWE-78] affecting multiple DrayTek VigorAP access point models. The flaw resides in the tr069TestInform function, which fails to filter dangerous characters in the event_code field before concatenating it into a system command. An authenticated remote attacker with administrative credentials can execute arbitrary commands with root privileges on the affected device. The vulnerability is reachable through the device's web management interface over the network.
Critical Impact
Successful exploitation grants root-level command execution on affected DrayTek VigorAP devices, allowing full compromise of the access point and any traffic it handles.
Affected Products
- DrayTek VigorAP series access points (multiple models)
- Devices exposing the TR-069 test inform functionality via the web management interface
- Refer to the DrayTek Security Advisory for the full list of affected models and firmware versions
Discovery Timeline
- 2026-08-24 - CVE-2026-71904 published to NVD
- 2026-08-26 - Last updated in NVD database
Technical Details for CVE-2026-71904
Vulnerability Analysis
The vulnerability exists within the tr069TestInform handler on DrayTek VigorAP devices. This function is part of the device's TR-069 client testing interface, which allows administrators to trigger inform messages to a configured Auto Configuration Server (ACS). The handler accepts an event_code parameter from the web management interface and passes it into a system command without adequate input validation.
Because the event_code field is concatenated directly into a shell command string, an attacker can inject shell metacharacters such as ;, |, &, or backticks to break out of the intended argument context. The resulting command runs under the web server process, which executes as root on VigorAP firmware. Exploitation requires valid administrator credentials, so the flaw is most dangerous when devices use default, weak, or reused credentials, or when management interfaces are exposed to untrusted networks.
Root Cause
The root cause is insufficient input sanitization before shell command construction. The tr069TestInform function does not enforce an allowlist for the event_code value and does not escape or reject shell metacharacters. This is a classic instance of CWE-78: Improper Neutralization of Special Elements used in an OS Command.
Attack Vector
An authenticated attacker sends a crafted HTTP request to the web management endpoint that invokes tr069TestInform. The request supplies an event_code value containing shell metacharacters and an appended command payload. The device's backend concatenates the value into its command string and executes it via a shell, running the injected payload as root. Full technical details are documented in the VulnCheck advisory.
No verified proof-of-concept code has been published. The vulnerability mechanism is described in prose per the referenced advisories.
Detection Methods for CVE-2026-71904
Indicators of Compromise
- Unexpected HTTP POST requests to TR-069 test-inform endpoints on VigorAP devices containing shell metacharacters (;, |, &, backticks) in the event_code parameter
- New or unfamiliar processes spawned by the VigorAP web server, such as sh, wget, curl, or tftp invocations originating from the management daemon
- Outbound connections from VigorAP devices to unknown hosts, particularly on ports commonly used to stage payloads (TFTP/69, HTTP/80, HTTPS/443)
- Modifications to device configuration, firmware, or persistence locations that were not initiated by an authorized administrator
Detection Strategies
- Inspect HTTP request logs on the VigorAP management interface for tr069TestInform requests whose event_code field contains non-alphanumeric characters
- Correlate administrative logins with subsequent process execution and outbound network activity from the access point
- Deploy network intrusion detection signatures that flag command injection patterns targeting DrayTek management URIs
Monitoring Recommendations
- Forward VigorAP syslog and management-interface access logs to a centralized SIEM for retention and analysis
- Alert on authentication anomalies against the VigorAP web UI, including brute-force attempts and logins from unexpected source IPs
- Monitor for outbound egress from access-point management interfaces, which should generally not initiate connections to arbitrary internet hosts
How to Mitigate CVE-2026-71904
Immediate Actions Required
- Apply the firmware update from DrayTek as documented in the DrayTek Security Advisory
- Restrict access to the VigorAP web management interface to trusted management networks only; do not expose it to the internet
- Rotate all administrative credentials on affected devices and enforce strong, unique passwords
- Audit device configurations and logs for signs of unauthorized command execution before patching
Patch Information
DrayTek has issued firmware updates for affected VigorAP models. Administrators should consult the vendor advisory for the specific fixed firmware version corresponding to each model and upgrade all managed devices. Follow the vendor's documented upgrade procedure, and verify firmware integrity after installation.
Workarounds
- Disable remote access to the web management interface until patches are applied
- Place VigorAP management interfaces behind a dedicated management VLAN with strict ACLs limiting access to authorized administrator workstations
- Require VPN access for any remote administration of the devices
- Monitor and rate-limit authentication attempts against the management interface to reduce credential-based exposure
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
