CVE-2026-77946 Overview
CVE-2026-77946 is a stack-based buffer overflow in the TRENDnet TEW-821DAP wireless access point running firmware version 2.2.01b05. The flaw resides in the uci_safe_get function inside /cgi-bin/apply_time.cgi, part of the NTP Timezone Configuration Handler. Attackers can manipulate the system.ntp.server, system.ntp.enable_server, cameo.time.time_zone, or cameo.cameo.syslog_server arguments to trigger memory corruption. The attack is remote, requires no authentication, and no user interaction. Public disclosure of the exploit details increases the risk of active weaponization against exposed devices.
Critical Impact
Unauthenticated remote attackers can corrupt stack memory on TRENDnet TEW-821DAP devices, potentially achieving arbitrary code execution and full device takeover.
Affected Products
- TRENDnet TEW-821DAP firmware version 2.2.01b05
- /cgi-bin/apply_time.cgi NTP Timezone Configuration Handler
- uci_safe_get function processing NTP and syslog configuration parameters
Discovery Timeline
- 2026-08-22 - CVE-2026-77946 published to NVD
- 2026-08-26 - Last updated in NVD database
Technical Details for CVE-2026-77946
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 component is the NTP Timezone Configuration Handler exposed through the CGI endpoint /cgi-bin/apply_time.cgi. The uci_safe_get helper retrieves configuration values from the Unified Configuration Interface (UCI) subsystem without enforcing destination buffer bounds. Attackers supply oversized values for the NTP server, timezone, or syslog parameters to overflow a fixed-size stack buffer. Because the endpoint is reachable over the network and does not require authentication, exploitation can be performed remotely against any device exposing the management interface.
Root Cause
The root cause is missing length validation in the uci_safe_get routine when copying user-controlled configuration values into a stack buffer. The function trusts input drawn from the request without bounding the copy to the destination size, allowing adjacent stack frames, saved registers, and the return address to be overwritten.
Attack Vector
A remote attacker sends a crafted HTTP request to /cgi-bin/apply_time.cgi with an oversized value in one of the affected parameters: system.ntp.server, system.ntp.enable_server, cameo.time.time_zone, or cameo.cameo.syslog_server. The oversized value flows through uci_safe_get and overflows the stack buffer. Successful exploitation can crash the device or, with tailored payloads, redirect execution to attacker-controlled code. Public proof-of-concept material is referenced in the GitHub write-up and the VulDB entry.
Detection Methods for CVE-2026-77946
Indicators of Compromise
- HTTP POST requests to /cgi-bin/apply_time.cgi containing unusually long values in system.ntp.server, system.ntp.enable_server, cameo.time.time_zone, or cameo.cameo.syslog_server parameters.
- Unexpected reboots, watchdog resets, or crash logs on TEW-821DAP devices following management-interface traffic.
- Outbound connections from the access point to unknown hosts, indicating post-exploitation callbacks.
Detection Strategies
- Deploy network intrusion detection signatures that flag requests to apply_time.cgi with parameter values exceeding expected lengths (for example, over 256 bytes).
- Monitor for repeated requests to the NTP timezone configuration endpoint from external or non-administrative source addresses.
- Correlate device crash telemetry with inbound HTTP traffic to the CGI management interface.
Monitoring Recommendations
- Forward device syslog and web-server access logs to a centralized logging platform for anomaly analysis.
- Track configuration changes and firmware versions across the wireless-access-point fleet to identify vulnerable units.
- Alert on any exposure of the TEW-821DAP management interface to untrusted networks or the public internet.
How to Mitigate CVE-2026-77946
Immediate Actions Required
- Restrict access to the TEW-821DAP web management interface to trusted management VLANs and administrator workstations only.
- Block internet-facing exposure of the device management ports at the perimeter firewall.
- Inventory all TEW-821DAP units running firmware 2.2.01b05 and schedule remediation.
- Reset device credentials and review configuration for unauthorized changes on devices previously exposed to untrusted networks.
Patch Information
At the time of publication, no vendor patch is referenced in the NVD entry for CVE-2026-77946. Administrators should monitor the TRENDnet support portal and the VulDB advisory for firmware updates addressing the uci_safe_get bounds issue.
Workarounds
- Disable remote administration and confine the management interface to a dedicated administrative network.
- Place vulnerable access points behind a reverse proxy or web application firewall that enforces strict parameter length limits on /cgi-bin/apply_time.cgi.
- Segment IoT and infrastructure devices from user and server networks to limit lateral movement in the event of compromise.
- If no compensating controls are feasible, retire and replace affected devices with supported hardware running current firmware.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
