HTB-Redeemer-Write-up

6 min readNov 19, 2024

Databases are a collection of organized information that can be easily accessed.

Introduction
Databases are a collection of organized information that can be easily accessed, managed and updated. In
most environments, database systems are very important because they communicate information related
to your sales transactions, product inventory, customer profiles and marketing activities.
There are different types of databases and one among them is Redis, which is an ‘in-memory’ database.

In-memory databases are the ones that rely essentially on the primary memory for data storage (meaning that
the database is managed in the RAM of the system); in contrast to databases that store data on the disk or
SSDs.

As the primary memory is significantly faster than the secondary memory, the data retrieval time in
the case of ‘in-memory’ databases is very small, thus offering very efficient & minimal response times.
In-memory databases like Redis are typically used to cache data that is frequently requested for quick
retrieval. For example, if there is a website that returns some prices on the front page of the site.

The website may be written to first check if the needed prices are in Redis, and if not, then check the traditional
database (like MySQL or MongoDB).

When the value is loaded from the database, it is then stored in Redis
for some shorter period of time (seconds or minutes or hours), to handle any similar requests that arrive
during that timeframe.

For a site with lots of traffic, this configuration allows for much faster retrieval for the
majority of requests, while still having stable long term storage in the main database.
This lab focuses on enumerating a Redis server remotely and then dumping its database in order to retrieve the flag.

In this process, we learn about the usage of the redis-cli command line utility which helps
interact with the Redis service.

We also learn about some basic redis-cli commands, which are used to
interact with the Redis server and the key-value database.
Let us now dive straight into the lab.

Enumeration
In order to verify the connectivity & availability of the target, we can run the ping command with the IP
address of the target machine. After two successful replies, we can interrupt the ping command, as we are
satisfied with the connection quality. We do not always need to run commands for a long time. Sometimes,
getting a snippet of the result or an overview instead of a detailed report is more time-efficient than the
alternative.

Immediately after, we can follow up with a preliminary scan of the target. Using nmap with the appropriate
service version detection switch, we scan the IP address for any open ports and services.

-sV : Probe open ports to determine service/version info

What is Redis?
Redis (REmote DIctionary Server) is an open-source advanced NoSQL key-value data store used as a database, cache, and message broker. The data is stored in a dictionary format having key-value pairs.

It is typically used for short term storage of data that needs fast retrieval. Redis does backup data to hard drives
to provide consistency.
The server Redis runs as server-side software so its core functionality is in its server component. The server listens for
connections from clients, programmatically or through the command-line interface.

The CLI
The command-line interface (CLI) is a powerful tool that gives you complete access to Redis’s data and its
functionalities if you are developing a software or tool that needs to interact with it.
Database
The database is stored in the server’s RAM to enable fast data access.

Redis also writes the contents of the database to disk at varying intervals to persist it as a backup, in case of failure.

Installing redis-cli Now, to be able to interact remotely with the Redis server, we need to download the redis-cli utility. It
can be downloaded using the following command :

sudo apt install redis-tools

Enumerating Redis Server
After successfully installing the redis-cli utility, let us view its help page by typing in the redis-cli — help command in our terminal to receive a list of all possible switches for the tool and their description.

redis-cli --help
Usage: redis-cli [OPTIONS] [cmd [arg [arg ...]]]
-h <hostname> Server hostname (default: 127.0.0.1).
-p <port> Server port (default: 6379).
-s <socket> Server socket (overrides hostname and port).
-a <password> Password to use when connecting to the server.
-r <repeat> Execute specified command N times.
-i <interval> When -r is used, waits <interval> seconds per command.
It is possible to specify sub-second times like -i 0.1.
-n <db> Database number.
-x Read last argument from STDIN.
-d <delimiter> Multi-bulk delimiter in for raw formatting (default: \n).
-c Enable cluster mode (follow -ASK and -MOVED redirections).
--raw Use raw formatting for replies (default when STDOUT is
not a tty).
--no-raw Force formatted output even when STDOUT is not a tty.
--csv Output in CSV format.
--stat Print rolling stats about server: mem, clients, ...
--latency Enter a special mode continuously sampling latency.
--latency-history Like --latency but tracking latency changes over time.
Default time interval is 15 sec. Change it using -i.
--latency-dist Shows latency as a spectrum, requires xterm 256 colors.
Default time interval is 1 sec. Change it using -i.
--lru-test <keys> Simulate a cache workload with an 80-20 distribution.
--slave Simulate a slave showing commands received from the master.
--rdb <filename> Transfer an RDB dump from remote server to local file.
--pipe Transfer raw Redis protocol from stdin to server.
--pipe-timeout <n> In --pipe mode, abort with error if after sending all data.
no reply is received within <n> seconds.
Default timeout: 30. Use 0 to wait forever.
--bigkeys Sample Redis keys looking for big keys.
--scan List all keys using the SCAN command.
--pattern <pat> Useful with --scan to specify a SCAN pattern.
--intrinsic-latency <sec> Run a test to measure intrinsic system latency.
The test will run for the specified amount of seconds.
--eval <file> Send an EVAL command using the Lua script at <file>.
--help Output this help and exit.
--version Output version and exit.

In our case, we will only need to use the following switch for specifying the host that we need to connect to :

-h <hostname> : specify the hostname of the target to connect to

Let us connect to the redis server using the following command :

The keyspace section provides statistics on the main dictionary of each database. The statistics include the
number of keys, and the number of keys with an expiration.
In our case, under the Keyspace section, we can see that only one database exists with index 0 .
Let us select this Redis logical database by using the select command followed by the index number of
the database that needs to be selected :