CVE-2026-76589 Overview
CVE-2026-76589 is a stack-based buffer overflow in the TRENDnet TEW-755AP wireless access point, affecting firmware releases up to build 20260702. The flaw resides in the function FUN_401000 inside the /sbin/mycli binary. An attacker who supplies an oversized ssid argument can overwrite adjacent stack memory, corrupting control data such as the saved return address. The issue is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). A public proof-of-concept exploit is available, and the attack can be launched over the network with low privileges.
Critical Impact
Successful exploitation can lead to arbitrary code execution on the access point, giving attackers control over the affected wireless infrastructure.
Affected Products
- TRENDnet TEW-755AP wireless access point
- Firmware builds up to and including 20260702
- The vulnerable component is the mycli binary located at /sbin/mycli
Discovery Timeline
- 2026-08-19 - CVE-2026-76589 published to the National Vulnerability Database
- 2026-08-20 - Last updated in NVD database
Technical Details for CVE-2026-76589
Vulnerability Analysis
The vulnerability is a classic stack-based buffer overflow inside function FUN_401000 of the /sbin/mycli command-line utility shipped with the TRENDnet TEW-755AP. The ssid argument passed to the function is copied into a fixed-size stack buffer without bounds validation. When the supplied value exceeds the buffer length, the copy operation overwrites the saved frame pointer and return address on the stack.
Because mycli handles configuration input reachable through remote management interfaces, an authenticated attacker with low privileges can trigger the overflow across the network. Depending on the binary's compilation options and the presence of stack protections, exploitation can range from denial of service to full arbitrary code execution on the device.
Root Cause
The root cause is missing input length validation before a string copy operation into a bounded stack buffer inside FUN_401000. The function trusts the length of the ssid argument and performs an unchecked copy, allowing adjacent stack memory to be overwritten.
Attack Vector
Exploitation occurs over the network against the device's management interface. The attacker submits an oversized ssid value to the mycli handler, corrupting the stack and hijacking control flow. A public proof-of-concept demonstrating the overflow is available in the researcher's GitHub PoC Script and the associated GitHub CVE Repository. Additional technical metadata is tracked in the VulDB CVE Detail entry.
Because verified exploitation code is limited to the referenced public PoC, no synthesized exploit code is reproduced here.
Detection Methods for CVE-2026-76589
Indicators of Compromise
- Unexpected crashes, restarts, or watchdog resets of the mycli process on TEW-755AP devices.
- Configuration change requests containing anomalously long ssid values, especially strings exceeding typical 32-character SSID limits.
- Outbound connections from the access point to unfamiliar hosts following a management-plane interaction.
Detection Strategies
- Inspect management-plane traffic for administrative requests containing oversized ssid parameters or non-printable byte sequences.
- Monitor device logs for repeated authentication events followed by process crashes involving /sbin/mycli.
- Correlate configuration API calls with subsequent loss of management-plane responsiveness.
Monitoring Recommendations
- Forward syslog output from TEW-755AP devices to a centralized log platform and alert on mycli crash signatures.
- Baseline expected SSID configuration payload sizes and flag deviations.
- Restrict and audit access to the device management interface, logging every authenticated session.
How to Mitigate CVE-2026-76589
Immediate Actions Required
- Restrict access to the TEW-755AP management interface to trusted administrative networks only.
- Rotate administrative credentials to reduce the risk of low-privileged accounts being abused for exploitation.
- Review recent configuration changes on affected devices for anomalous ssid values.
Patch Information
At the time of publication, no vendor advisory URL is listed in the NVD entry. Administrators should monitor the TRENDnet support portal for firmware updates addressing CVE-2026-76589 and consult the VulDB Vulnerability Info page for updates on remediation status.
Workarounds
- Disable remote management access to the device and administer it only over a physically isolated network.
- Place affected access points behind a firewall that restricts inbound traffic to the management port to a known administrative jump host.
- If feasible, replace vulnerable units with supported hardware until a validated firmware patch is released.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
