add Yealink_Device_Management_Platform_SSRF_CVE_2021_27561

Yealink/CVE-2021-27561/README.md

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+# Yealink Device Management Platform SSRF (CVE-2021-27561)
+
+Yealink DM (Device Management) platform offers a comprehensive management solution with key features Unified Deployment and Management, Real-Time Monitoring and Alarm, Remote Troubleshooting. By chaining a pre-auth SSRF vulnerability and a command injection vulnerability, it is possible to execute commands as root without authentication against this product, by sending a simple HTTPS request to the remote target.
+
+**FOFA query rule**: [title="dm-v30"](https://fofa.so/result?qbase64=dGl0bGU9ImRtLXYzMCI%3D)
+
+# Demo
+
+![img](Yealink_Device_Management_Platform_SSRF_CVE_2021_27561.gif)
+