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We found out that many TLS implementations are still vulnerable to different variations of a 19-year old Bleichenbacher's attack. Since Hanno argued to have an attack name, we called it ROBOT: https://robotattack.org

Given the new attack variants, we released a new version of TLS-Attacker 2.2, which covers our vulnerabilities.

Bleichenbacher's attack from 1998

In 1998, Daniel Bleichenbacher discovered that the error messages given by SSL servers for errors in the PKCS #1 1.5 padding allow an adversary to execute an adaptive-chosen ciphertext attack. This attack also belongs to the category of padding oracle attacks. By performing the attack, the adversary exploits different responses returned by the server that decrypts the requests and validates the PKCS#1 1.5 padding. Given such a server, the attacker can use it as an oracle and decrypt ciphertexts.

We refer to one of our previous blog posts for more details.

OK, so what is new in our research?

In our research we performed scans of several well-known hosts and found out many of them are vulnerable to different forms of the attack. In the original paper, an oracle was constructed from a server that responded with different TLS alert messages. In 2014, further side-channels like timings were exploited. However, all the previous studies have considered mostly open source implementations. Only a few vulnerabilities have been found.

In our scans we could identify more than seven vulnerable products and open source software implementations, including F5, Radware, Cisco, Erlang, Bouncy Castle, or WolfSSL. We identified new side-channels triggered by incomplete protocol flows or TCP socket states.

For example, some F5 products would respond to a malformed ciphertext located in the ClientKeyExchange message with a TLS alert 40 (handshake failure) but allow connections to timeout if the decryption was successful. We could observe this behaviour only when sending incomplete TLS handshakes missing ChangeCipherSpec and Finished messages.

See our paper for more interesting results.

Release of TLS-Attacker 2.2

These new findings motivated us to implement the complete detection of Bleichenbacher attacks in our TLS-Attacker. Before our research, TLS-Attacker had implemented a basic Bleichenbacher attack evaluation with full TLS protocol flows. We extended this evaluation with shortened protocol flows with missing ChangeCipherSpec and Finished messages, and implemented an oracle detection based on TCP timeouts and duplicated TLS alerts. In addition, Robert (@ic0ns) added many fixes and merged features like replay attacks on 0-RTT in TLS 1.3.

You can find the newest version release here: https://github.com/RUB-NDS/TLS-Attacker/releases/tag/v2.2

TLS-Attacker allows you to automatically send differently formatted PKCS#1 encrypted messages and observe the server behavior:

$ java -jar Attacks.jar bleichenbacher -connect [host]:[port]

In case the server responds with different error messages, it is most likely vulnerable. The following example provides an example of a vulnerable server detection output:

14:12:42 [main] CONSOLE attacks.impl.Attacker - A server is considered vulnerable to this attack if it responds differently to the test vectors.
14:12:42 [main] CONSOLE attacks.impl.Attacker - A server is considered secure if it always responds the same way.
14:12:49 [main] CONSOLE attacks.impl.Attacker - Found a difference in responses in the Complete TLS protocol flow with CCS and Finished messages.
14:12:49 [main] CONSOLE attacks.impl.Attacker - The server seems to respond with different record contents.
14:12:49 [main] INFO  attacks.Main - Vulnerable:true

In this case TLS-Attacker identified that sending different PKCS#1 messages results in different server responses (the record contents are different).

Network Mapping (NMAP)

Basically NMAP stands for Network Mapping. A free open source tool used for scanning ports, service detection, operating system detection and IP address detection of the targeted machine. Moreover, it performs a quick and efficient scanning a large number of machines in a single session to gathered information about ports and system connected to the network. It can be used over UNIX, LINUX and Windows.

There are some terminologies which we should understand directly whenever we heard like Open ports, Filtered ports and Unfiltered ports.

Open Ports means the target machine accepts incoming request on that port cause these ports are used to accept packets due to the configuration of TCP and UDP.

Filtered ports means the ports are usually opened but due to firewall or network filtering the nmap doesn't detect the open ports.

Unfiltered means the nmap is unable to determine whether the port is open or filtered while the port is accessible.

Types Of NMAP Scan

Scan Type	Description
Null Scan	This scan is performed by both an ethical hackers and black hat hackers. This scan is used to identify the TCP port whether it is open or closed. Moreover, it only works over UNIX based systems.
TCP connect	The attacker makes a full TCP connection to the target system. There's an opportunity to connect the specifically port which you want to connect with. SYN/ACK signal observed for open ports while RST/ACK signal observed for closed ports.
ACK scan	Discovering the state of firewall with the help ACK scan whether it is stateful or stateless. This scan is typically used for the detection of filtered ports if ports are filtered. Moreover, it only works over the UNIX based systems.
Windows scan	This type of scan is similar to the ACK scan but there is ability to detect an open ports as well filtered ports.
SYN stealth scan	This malicious attack is mostly performed by attacker to detect the communication ports without making full connection to the network. This is also known as half-open scanning.

All NMAP Commands

Commands	Scan Performed
-sT	TCP connect scan
-sS	SYN scan
-sF	FIN scan
-sX	XMAS tree scan
-sN	Null scan
-sP	Ping scan
-sU	UDP scan
-sO	Protocol scan
-sA	ACK scan
-sW	Window scan
-sR	RPC scan
-sL	List/DNS scan
-sI	Idle scan
-Po	Don't ping
-PT	TCP ping
-PS	SYN ping
-PI	ICMP ping
-PB	ICMP and TCP ping
-PB	ICMP timestamp
-PM	ICMP netmask
-oN	Normal output
-oX	XML output
-oG	Greppable output
-oA	All output
-T Paranoid	Serial scan; 300 sec between scans
-T Sneaky	Serial scan; 15 sec between scans
-T Polite	Serial scan; .4 sec between scans
-T Normal	Parallel scan
-T Aggressive	Parallel scan, 300 sec timeout, and 1.25 sec/probe
-T Insane	Parallel scan, 75 sec timeout, and .3 sec/probe

How to Scan

You can perform nmap scanning over the windows command prompt followed by the syntax below. For example, If you wanna scan the host with the IP address 192.168.2.1 using a TCP connect scan type, enter this command:

nmap 192.168.2.1 –sT

nmap -sT 192.168.2.1

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Ddal

Recovering data from a backup should be an easy thing to do. At least this is what you expect. Yesterday I had a problem which should have been easy to solve, but it was not. I hope this blog post can help others who face the same problem.

The problem

1. I had an encrypted Time Machine backup which was not used for months
2. This backup was not on an official Apple Time Capsule or on a USB HDD, but on a WD MyCloud NAS
3. I needed files from this backup
4. After running out of time I only had SSH access to the macOS, no GUI

The struggle

By default, Time Machine is one of the best and easiest backup solution I have seen. As long as you stick to the default use case, where you have one active backup disk, life is pink and happy. But this was not my case.

As always, I started to Google what shall I do. One of the first options recommended that I add the backup disk to Time Machine, and it will automagically show the backup snapshots from the old backup. Instead of this, it did not show the old snapshots but started to create a new backup. Panic button has been pressed, backup canceled, back to Google.

Other tutorials recommend to click on the Time Machine icon and pressing alt (Option) key, where I can choose "Browse other backup disks". But this did not list the old Time Machine backup. It did list the backup when selecting disks in Time Machine preferences, but I already tried and failed that way.

YAT (yet another tutorial) recommended to SSH into the NAS, and browse the backup disk, as it is just a simple directory where I can see all the files. But all the files inside where just a bunch of nonsense, no real directory structure.

YAT (yet another tutorial) recommended that I can just easily browse the content of the backup from the Finder by double-clicking on the sparse bundle file. After clicking on it, I can see the disk image on the left part of the Finder, attached as a new disk.
Well, this is true, but because of some bug, when you connect to the Time Capsule, you don't see the sparse bundle file. And I got inconsistent results, for the WD NAS, double-clicking on the sparse bundle did nothing. For the Time Capsule, it did work.
At this point, I had to leave the location where the backup was present, and I only had remote SSH access. You know, if you can't solve a problem, let's complicate things by restrict yourself in solutions.

Finally, I tried to check out some data forensics blogs, and besides some expensive tools, I could find the solution.

The solution

Finally, a blog post provided the real solution - hdiutil.
The best part of hdiutil is that you can provide the read-only flag to it. This can be very awesome when it comes to forensics acquisition.

To mount any NAS via SMB:

mount_smbfs afp://<username>@<NAS_IP>/<Share_for_backup> /<mountpoint>

To mount a Time Capsule share via AFP:

mount_afp afp://any_username:password@<Time_Capsule_IP>/<Share_for_backup> /<mountpoint>

And finally this command should do the job:

hdiutil attach test.sparsebundle -readonly

It is nice that you can provide read-only parameter.

If the backup was encrypted and you don't want to provide the password in a password prompt, use the following:

printf '%s' 'CorrectHorseBatteryStaple' | hdiutil attach test.sparsebundle -stdinpass -readonly

Note: if you receive the error "resource temporarily unavailable", probably another machine is backing up to the device

And now, you can find your backup disk under /Volumes. Happy restoring!

Probably it would have been quicker to either enable the remote GUI, or to physically travel to the system and login locally, but that would spoil the fun.

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Sunday, August 30, 2020

TLS-Attacker V2.2 And The ROBOT Attack