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CVE-2026-19924 – Authentication Bypass – Tenda AC10 V4.0 (Firmware 16.03.10.09_multi_TDE01)

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Summary

CVE-2026-19924 is a critical authentication bypass vulnerability in the httpd web-management service of the Tenda AC10 V4.0 wireless router, specifically in the R7WebsSecurityHandler request-filtering function. The flaw allows a remote, unauthenticated attacker to reach protected configuration and administrative endpoints that should require a valid login session. It affects firmware version 16.03.10.09_multi_TDE01 and carries a critical severity rating (CVSS v3.1 base score 9.8 / CVSS v4.0 score 9.3).

Technical details

  • Root cause: R7WebsSecurityHandler, the first-priority request handler in httpd, maintains a whitelist of URL prefixes (e.g. /public/, /lang/) that may be accessed without authentication. The whitelist check is performed with strstr against portions of the raw request URL, including the query string, while downstream request handlers only evaluate the path component of the URL.
  • Trigger conditions: An attacker appends a whitelisted string as a query parameter to a normally protected request path (e.g. ?easy-ui-1.0.3.js or ?img/main-logo.png). The security handler matches the whitelisted substring in the query string and allows the request through, while the actual path is then processed by the target (protected) handler.
  • Attack vector: Network — the request can be sent to the device’s web management interface over the LAN, and over the WAN if remote management is enabled. No credentials, prior session, or user interaction are required.
  • Impact: Successful exploitation grants unauthenticated access to configuration download (/cgi-bin/DownloadCfg), system logs, firmware upgrade functionality, and administrative "set" endpoints controlling LAN, Wi-Fi, DHCP, DNS, and VPN settings — effectively full administrative takeover of the device.

Affected software

  • Tenda AC10 V4.0, firmware US_AC10V4.0si_V16.03.10.09_multi_TDE01

Severity

  • CVSS v3.1: 9.8 (Critical) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • CVSS v4.0: 9.3 (Critical) — CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: At the time of publication, no vendor patch or updated firmware addressing this specific authentication bypass has been confirmed as available from Tenda. Security teams should check Tenda’s official download portal for the AC10 V4.0 model regularly for a fixed firmware build and apply it as soon as it is released.
  • Network mitigations (no patch available):
    • Disable remote/WAN access to the router’s web management interface immediately.
    • Restrict access to the management interface to trusted LAN hosts only (e.g., via firewall/ACL rules or a dedicated management VLAN).
    • Treat any internet-exposed Tenda AC10 management interface as high risk and prioritize it for isolation or replacement until a fix is confirmed.
    • Monitor for anomalous unauthenticated requests to configuration/download endpoints containing suspicious query-string parameters as a possible indicator of exploitation attempts.

References

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