D-LINK DIR-3040 Libcli test environment hard-coded password vulnerability [CVE-2021-21820]

CVE number – CVE-2021-21820

A hard-coded password vulnerability exists in the Libcli Test Environment functionality of D-LINK DIR-3040 1.13B03. A specially crafted network request can lead to code execution. An attacker can send a sequence of requests to trigger this vulnerability.

Tested Versions

D-LINK DIR-3040 1.13B03

The DIR-3040 is an AC3000-based wireless internet router.

A hidden telnet service can be started without authentication by visiting


Discovered by Dave McDaniel of Cisco Talos.

Duncan Newell

Duncan is a technology professional with over 20 years experience of working in various IT roles. He has a interest in cyber security, and has a wide range of other skills in radio, electronics and telecommunications.

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