CVE-2026-76590: TRENDnet TEW-755AP Buffer Overflow Flaw

CVE-2026-76590 Overview

CVE-2026-76590 is a stack-based buffer overflow affecting TRENDnet TEW-755AP wireless access points through firmware version 20260702. The flaw resides in the ssi component, specifically in the /cgi-bin/wan.cgi handler. Attackers can trigger the overflow by manipulating the cameo.wan.wan_pppoe_password_00 argument. The vulnerability is exploitable over the network and requires only low privileges. A public proof-of-concept exploit is available, increasing the risk of opportunistic attacks against exposed devices.

Critical Impact
Remote attackers with low privileges can corrupt stack memory in wan.cgi and potentially achieve arbitrary code execution on affected TRENDnet TEW-755AP devices.

Affected Products

TRENDnet TEW-755AP wireless access point
Firmware versions up to and including 20260702
The ssi component processing /cgi-bin/wan.cgi requests

Discovery Timeline

2026-08-19 - CVE-2026-76590 published to NVD
2026-08-20 - Last updated in NVD database

Technical Details for CVE-2026-76590

Vulnerability Analysis

The vulnerability is a stack-based buffer overflow classified under [CWE-119]: Improper Restriction of Operations within the Bounds of a Memory Buffer. The affected code path handles WAN configuration requests submitted to /cgi-bin/wan.cgi through the Server Side Includes (SSI) processing component. The cameo.wan.wan_pppoe_password_00 parameter, which stores the PPPoE authentication password, is copied into a fixed-size stack buffer without adequate length validation.

Supplying an oversized value for this parameter overflows the destination buffer and corrupts adjacent stack memory, including the saved return address. Successful exploitation can redirect execution flow and lead to arbitrary code execution in the context of the CGI process, typically running with elevated privileges on embedded appliances.

Root Cause

The root cause is missing bounds checking when the CGI handler processes the PPPoE password argument. The handler likely uses an unsafe string copy routine such as strcpy or sprintf against a stack-allocated buffer. No length validation is performed on user-supplied input before the copy operation.

Attack Vector

Exploitation is performed remotely over the network by sending a crafted HTTP request to the device's management interface. The attacker must have low-level authentication to reach the /cgi-bin/wan.cgi endpoint. A public proof-of-concept script demonstrating the overflow is available in the GitHub PoC Repository.

The vulnerability mechanism is straightforward: the attacker crafts an HTTP POST request to /cgi-bin/wan.cgi with an oversized cameo.wan.wan_pppoe_password_00 value that exceeds the destination buffer size, overwriting the return address on the stack. See the GitHub Source Code for full technical details.

Detection Methods for CVE-2026-76590

Indicators of Compromise

HTTP POST requests to /cgi-bin/wan.cgi containing abnormally long values for the cameo.wan.wan_pppoe_password_00 parameter.
Unexpected crashes, reboots, or watchdog resets of the TEW-755AP device shortly after receiving external HTTP traffic.
New or unauthorized outbound network connections originating from the access point management plane.
Web server error log entries referencing wan.cgi with malformed or truncated request data.

Detection Strategies

Inspect HTTP traffic to the device management interface and flag requests where PPPoE-related parameters exceed reasonable length thresholds (for example, more than 128 bytes).
Correlate CGI request patterns with subsequent device unavailability or configuration drift to identify exploitation attempts.
Deploy network intrusion detection signatures that match oversized parameter values targeting /cgi-bin/wan.cgi.

Monitoring Recommendations

Restrict and monitor administrative access to the TEW-755AP web interface, alerting on access from untrusted network segments.
Log and review all authentication events against the device to identify brute-force or credential-reuse activity that could satisfy the low-privilege requirement.
Track outbound connections from access points, which normally do not initiate external sessions.

How to Mitigate CVE-2026-76590

Immediate Actions Required

Remove the TEW-755AP management interface from any internet-exposed network segment and restrict access to trusted administrative hosts only.
Rotate all administrative and PPPoE credentials on affected devices to reduce the risk of low-privilege access being obtained.
Audit device configurations for unauthorized changes and reset devices suspected of compromise to factory defaults before reconfiguring.
Monitor vendor channels for a firmware update addressing the flaw and apply it as soon as it is released.

Patch Information

As of the last NVD update on 2026-08-20, no vendor patch has been referenced in public advisories for CVE-2026-76590. Administrators should consult the VulDB CVE Details entry and TRENDnet's official support channels for firmware update availability.

Workarounds

Place the device management interface behind a firewall or VPN and block HTTP/HTTPS access from untrusted networks.
Disable remote management if the feature is not required for operations.
Apply access control lists (ACLs) on upstream network devices to permit management traffic only from known administrative IP addresses.
Consider replacing internet-facing TEW-755AP units with patched or supported hardware if a vendor fix is not made available.

bash

# Example: restrict access to the device management interface using iptables on an upstream gateway
iptables -A FORWARD -p tcp -d <TEW-755AP-IP> --dport 80 -s <admin-subnet> -j ACCEPT
iptables -A FORWARD -p tcp -d <TEW-755AP-IP> --dport 443 -s <admin-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 -j DROP