CVE-2026-77945: TRENDnet TEW-821DAP RCE Vulnerability

CVE-2026-77945 Overview

CVE-2026-77945 is a command injection vulnerability affecting the TRENDnet TEW-821DAP wireless access point running firmware version 2.2.01b05. The flaw resides in an unknown function within the /cgi-bin/upload.cgi file, part of the device's Server Side Includes (SSI) component. Attackers can manipulate the filename argument to inject arbitrary operating system commands. The vulnerability is remotely reachable over the network and requires low-level privileges to exploit. Public exploit details have been released, increasing the likelihood of opportunistic abuse against exposed devices. The issue is classified under CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component).

Critical Impact
Authenticated network-adjacent attackers can inject shell commands through the filename parameter of upload.cgi, gaining execution on the access point.

Affected Products

TRENDnet TEW-821DAP wireless access point
Firmware version 2.2.01b05
The ssi component and /cgi-bin/upload.cgi handler

Discovery Timeline

2026-08-22 - CVE-2026-77945 published to the National Vulnerability Database (NVD)
2026-08-25 - Last updated in NVD database

Technical Details for CVE-2026-77945

Vulnerability Analysis

The vulnerability exists in the file upload handler /cgi-bin/upload.cgi on the TRENDnet TEW-821DAP. The handler processes the filename argument supplied by the client but fails to neutralize shell metacharacters before passing the value to a downstream command interpreter. As a result, attacker-controlled input reaches a shell context and executes as commands on the device. According to the vendor description, the exploit has been made public, which typically increases opportunistic scanning against exposed management interfaces. The Exploit Prediction Scoring System (EPSS) rates the probability of exploitation at 1.284% with a percentile of 68.

Root Cause

The root cause is improper neutralization of special elements passed to a downstream component (CWE-74). The upload.cgi script embeds the filename value into a system call or shell command without sanitization or safe argument passing. Shell control characters such as ;, |, &, and backticks are interpreted by the underlying shell rather than treated as literal filename bytes.

Attack Vector

Exploitation occurs over the network against the device's HTTP management service. An attacker with low-level privileges submits a crafted request to /cgi-bin/upload.cgi where the filename parameter contains a shell command payload appended to a benign filename. The injected command executes with the privileges of the CGI process, typically root on embedded devices. The vulnerability manifests server-side and does not require user interaction. Refer to the GitHub command injection report for the parameter format and reproduction steps.

Detection Methods for CVE-2026-77945

Indicators of Compromise

HTTP POST or GET requests to /cgi-bin/upload.cgi containing shell metacharacters (;, |, &, backticks, $()) inside the filename parameter.
Outbound connections from the access point to unexpected external hosts, indicating post-exploitation command execution or reverse shells.
New processes, cron entries, or writable files on the device that were not created by the vendor firmware.

Detection Strategies

Inspect web server and reverse-proxy logs upstream of the device for anomalous filename values submitted to upload.cgi.
Deploy network intrusion detection signatures that flag common command injection patterns targeting embedded HTTP endpoints.
Correlate management-plane HTTP requests with subsequent outbound traffic from the same device to identify unexpected callbacks.

Monitoring Recommendations

Continuously monitor administrative access to TEW-821DAP devices and alert on requests from non-management subnets.
Track firmware versions across the fleet and flag any device still running 2.2.01b05.
Log DNS queries originating from access points and alert on lookups to newly observed or non-vendor domains.

How to Mitigate CVE-2026-77945

Immediate Actions Required

Restrict access to the TEW-821DAP management interface to trusted administrative networks using firewall or VLAN segmentation.
Change default administrative credentials and enforce strong passwords, since exploitation requires authentication at a low privilege level.
Audit the affected devices for signs of prior exploitation before applying any remediation, including checking for unauthorized files and configuration changes.

Patch Information

At the time of publication, no vendor advisory or firmware update addressing CVE-2026-77945 has been referenced in the enriched CVE data. Administrators should monitor the TRENDnet support portal and the VulDB entry for CVE-2026-77945 for updated firmware and vendor guidance.

Workarounds

Disable remote management on the WAN interface and block inbound access to the HTTP/HTTPS management ports from untrusted networks.
Place affected access points behind a network segmentation boundary and require VPN access for administrative operations.
If the device is not required, decommission it and replace with a supported model that receives active security maintenance.

bash

# Example: restrict management access to a trusted admin subnet on an upstream firewall
iptables -A FORWARD -p tcp -d <TEW-821DAP-IP> --dport 80  -s 10.0.99.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d <TEW-821DAP-IP> --dport 443 -s 10.0.99.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d <TEW-821DAP-IP> --dport 80  -j DROP
iptables -A FORWARD -p tcp -d <TEW-821DAP-IP> --dport 443 -j DROP