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CVE-2026-77946 – Remote Code Execution via Stack-Based Buffer Overflow – TRENDnet TEW-821DAP 2.2.01b

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Summary

CVE-2026-77946 is a critical, unauthenticated stack-based buffer overflow vulnerability in the TRENDnet TEW-821DAP wireless access point running firmware 2.2.01b05. The flaw resides in the uci_safe_get function used by the NTP Timezone Configuration Handler (/cgi-bin/apply_time.cgi), and can be triggered remotely over the network without authentication. It carries the maximum CVSS v3.1 base score of 10.0 (Critical) and a public proof-of-concept exploit is available.

Technical details

  • Root cause: The uci_safe_get function reads user-controlled UCI configuration parameters and copies them into fixed-size stack buffers using an unbounded copy operation, without validating input length.
  • Trigger conditions: An attacker sends a crafted HTTP POST request to /cgi-bin/apply_time.cgi, supplying an oversized value in one of the parameters system.ntp.server, system.ntp.enable_server, cameo.time.time_zone, or cameo.cameo.syslog_server.
  • Attack vector: Network-based, no authentication or user interaction required, low attack complexity.
  • Impact: Overwriting the saved return address on the stack allows an attacker to redirect program execution, potentially achieving arbitrary code execution with root/service privileges on the device, and can otherwise crash the affected service (denial of service).

Affected software

  • TRENDnet TEW-821DAP, firmware version 2.2.01b05 (component: NTP Timezone Configuration Handler / /cgi-bin/apply_time.cgi)

Severity

CVSS v3.1 Base Score: 10.0 (Critical)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: No official TRENDnet patch or firmware update addressing CVE-2026-77946 has been identified at this time. Check the TRENDnet support/downloads page for the TEW-821DAP for any newer firmware release and apply it as soon as it becomes available.
  • If no patch: Restrict access to the device’s management/configuration interface (/cgi-bin/apply_time.cgi and related CGI endpoints) to trusted internal networks only; do not expose the administrative interface directly to the internet. Place the device behind a firewall or VPN, disable remote/WAN administration if enabled, and monitor for anomalous POST requests to time/NTP configuration endpoints. Given the device is discontinued/end-of-life for related hardware revisions, evaluate replacing the access point with a currently supported model.

References

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