Stack-based Buffer Overflow in TRENDnet TEW-755AP Access Points

A critical security vulnerability has been identified in the TRENDnet TEW-755AP wireless access point, affecting all firmware versions up to 20260702. The flaw resides within the function FUN_401000 of the /sbin/mycli binary, which fails to properly validate the length of the 'ssid' input argument. By providing an overly long string as the SSID, an attacker can trigger a stack-based buffer overflow. This vulnerability allows for remote execution of arbitrary code with the privileges of the mycli process. Given the availability of public proof-of-concept exploit code, the risk of active exploitation against vulnerable network infrastructure is high. Organizations utilizing these devices should prioritize patching or network isolation to mitigate potential remote compromise.

Attack Chain

1. Attacker performs network discovery to identify reachable TRENDnet TEW-755AP management interfaces.
2. Attacker establishes a connection to the device's management service (typically via HTTP or internal management API).
3. Attacker identifies the endpoint handling configuration changes related to wireless network settings.
4. Attacker constructs a malicious request containing an oversized 'ssid' parameter designed to overwrite adjacent stack memory.
5. Attacker transmits the crafted request to the target device, invoking the vulnerable FUN_401000 function.
6. The /sbin/mycli binary attempts to copy the excessive 'ssid' data into a fixed-length buffer on the stack.
7. Buffer overflow occurs, overwriting the return address or function pointers within the stack frame.
8. Execution flow is hijacked, resulting in arbitrary command execution or process crash depending on the exploit payload.

Impact

Successful exploitation of CVE-2026-76589 results in a complete compromise of the wireless access point. Attackers can achieve remote code execution, allowing them to gain persistence, pivot deeper into the internal network, intercept wireless traffic, or cause a denial-of-service condition by crashing the system binary. This vulnerability is critical for environments relying on these access points as part of their edge network security.

Recommendation

• Immediately isolate all TRENDnet TEW-755AP devices from the public internet to prevent remote access by unauthorized parties.
• Audit network perimeter logs for unusual traffic targeting the management interfaces of wireless network hardware.
• Apply manufacturer-provided firmware updates that address the buffer overflow in the /sbin/mycli binary.
• Monitor internal network traffic for anomalous connection attempts or payload delivery patterns directed at embedded network devices.