CVE-2026-76591: TRENDnet TEW-755AP RCE Vulnerability

CVE-2026-76591 Overview

CVE-2026-76591 is a command injection vulnerability affecting the TRENDnet TEW-755AP wireless access point through firmware version 20260702. The flaw resides in the log_email_server function of the /cgi-bin/email.cgi script within the Server Side Includes (SSI) component. An authenticated remote attacker can manipulate input to inject arbitrary operating system commands. Public proof-of-concept exploit code is available, increasing the likelihood of opportunistic attacks against exposed devices. The weakness is categorized under [CWE-74] (Improper Neutralization of Special Elements in Output Used by a Downstream Component).

Critical Impact
Authenticated attackers can execute arbitrary commands on the underlying operating system of the affected access point, leading to full device compromise.

Affected Products

TRENDnet TEW-755AP Wireless Access Point
Firmware versions up to and including 20260702
Affected component: /cgi-bin/email.cgi SSI handler

Discovery Timeline

2026-08-19 - CVE-2026-76591 published to NVD
2026-08-20 - Last updated in NVD database

Technical Details for CVE-2026-76591

Vulnerability Analysis

The vulnerability exists in the log_email_server function within /cgi-bin/email.cgi, part of the SSI component on the TRENDnet TEW-755AP. The CGI handler processes user-supplied parameters related to email server logging configuration without sufficient sanitization. Because the input is passed to a downstream shell or command interpreter, an attacker can embed shell metacharacters to execute arbitrary commands. The device runs the injected commands with the privileges of the CGI process, which typically operate at elevated levels on embedded network appliances. Successful exploitation results in code execution on the access point, enabling attackers to modify configurations, capture traffic, or pivot into adjacent network segments.

Root Cause

The root cause is improper neutralization of special elements passed to a downstream component [CWE-74]. Input handled by the log_email_server function is concatenated into a command string without escaping or allow-list validation. Any shell metacharacter supplied by the requester is interpreted by the underlying shell rather than treated as literal data.

Attack Vector

The attack is delivered remotely over the network to the device's HTTP management interface. The attacker must possess low-privilege credentials to reach the vulnerable CGI endpoint. Once authenticated, the attacker submits a crafted HTTP request to /cgi-bin/email.cgi targeting the log_email_server parameter. A public proof of concept is published at the GitHub PoC Repository, demonstrating the injection technique against the SSI handler.

Refer to the VulDB Vulnerability Report for additional technical detail; no verified exploit code snippet is reproduced here.

Detection Methods for CVE-2026-76591

Indicators of Compromise

Unusual HTTP POST or GET requests to /cgi-bin/email.cgi containing shell metacharacters such as ;, |, &&, or backticks in email server parameters.
Unexpected outbound network connections initiated by the TEW-755AP device to unfamiliar hosts.
Configuration changes to the access point that were not initiated by an administrator.

Detection Strategies

Inspect HTTP traffic to the management interface for parameter values containing command separators or encoded shell syntax.
Correlate authentication events on the access point with subsequent CGI requests targeting email.cgi.
Monitor for the appearance of new processes or persistence mechanisms on the device via syslog forwarding where supported.

Monitoring Recommendations

Forward device syslog output to a centralized logging platform for retention and analysis.
Alert on any administrative access to the TEW-755AP web interface from networks outside expected management segments.
Baseline normal outbound traffic from access points and flag deviations, particularly connections to non-corporate destinations.

How to Mitigate CVE-2026-76591

Immediate Actions Required

Restrict access to the TEW-755AP web management interface to trusted management VLANs or IP allow-lists.
Rotate all administrative credentials on affected devices and enforce strong, unique passwords.
Remove any exposure of the device management interface from the public internet.
Audit access logs for prior interaction with the /cgi-bin/email.cgi endpoint.

Patch Information

At the time of publication, no vendor patch has been referenced in the available advisory data. Consult the VulDB CVE Details page and TRENDnet's official support channels for firmware updates addressing this issue. Apply any released firmware update as soon as it becomes available.

Workarounds

Place the access point behind a firewall that blocks inbound access to management ports from untrusted networks.
Disable remote administration features where they are not required for operations.
Segment the access point into a dedicated management network to reduce blast radius in the event of compromise.

bash

# Example: restrict management interface access with iptables on an upstream gateway
iptables -A FORWARD -p tcp -d <TEW-755AP_IP> --dport 80 -s <MGMT_SUBNET> -j ACCEPT
iptables -A FORWARD -p tcp -d <TEW-755AP_IP> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <TEW-755AP_IP> --dport 443 -s <MGMT_SUBNET> -j ACCEPT
iptables -A FORWARD -p tcp -d <TEW-755AP_IP> --dport 443 -j DROP