SALUD

viernes, 22 de mayo de 2020

[Guide] Finding Best Security Outsourcing Alternative For Your Organization

As cyberattacks continue to proliferate in volume and increase in sophistication, many organizations acknowledge that some part of their breach protection must be outsourced, introducing a million-dollar question of what type of service to choose form. Today, Cynet releases the Security Outsourcing Guide (download here), providing IT Security executives with clear and actionable guidance on

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SigPloit SS7 Tool

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jueves, 21 de mayo de 2020

Trendnet Cameras - I Always Feel Like Somebody'S Watching Me.

Firstly this post requires the following song to be playing.

http://www.youtube.com/watch?v=wVfjwIyc-CU

Now that we got that out of the way... I have been seeing posts on sites with people having fun with embedded systems/devices and I was feeling left out. I didn't really want to go out and buy a device so I looked at what was laying around.

Enter the Trendnet TV-IP110w - http://www.trendnet.com/products/proddetail.asp?prod=145_TV-IP110W

To start off the latest firmware for this device can be found at the following location :

http://downloads.trendnet.com/tv-ip110w/firmware/FW_TV-IP110W_A1.x(1.1.0.104).zip

First order of business was to update the camera with the most recent firmware:

Device info page confirming firmware version

Now that the device was using the same version of firmware as I was going to dive into, lets get to work. I will be using binwalk to fingerprint file headers that exist inside the firmware file. Binwalk can be downloaded from the following url: http://code.google.com/p/binwalk/

Running binwalk against the firmware file

binwalk FW_TV-IP110W_1.1.0-104_20110325_r1006.pck
DECIMAL HEX DESCRIPTION
-------------------------------------------------------------------------------------------------------
32320 0x7E40 gzip compressed data, from Unix, last modified: Thu Mar 24 22:59:08 2011, max compression
679136 0xA5CE0 gzip compressed data, was "rootfs", from Unix, last modified: Thu Mar 24 22:59:09 2011, max compression

Looks like there are two gzip files in the "pck" file. Lets carve them out using 'dd'. First cut the head off the file and save it off as '1_unk'

#dd if=FW_TV-IP110W_1.1.0-104_20110325_r1006.pck of=1_unk bs=1 count=32320
32320+0 records in
32320+0 records out
32320 bytes (32 kB) copied, 0.167867 s, 193 kB/s

Next cut out the first gzip file that was identified, we will call this file '2'

#dd if=FW_TV-IP110W_1.1.0-104_20110325_r1006.pck of=2 bs=1 skip=32320 count=646816
646816+0 records in
646816+0 records out
646816 bytes (647 kB) copied, 2.87656 s, 225 kB/s

Finally cut the last part of the file out that was identified as being a gzip file, call this file '3'

#dd if=FW_TV-IP110W_1.1.0-104_20110325_r1006.pck of=3 bs=1 skip=679136
2008256+0 records in
2008256+0 records out
2008256 bytes (2.0 MB) copied, 8.84203 s, 227 kB/s

For this post I am going to ignore files '1_unk' and '2' and just concentrate on file '3' as it contains an interesting bug :) Make a copy of the file '3' and extract it using gunzip

#file 3
3: gzip compressed data, was "rootfs", from Unix, last modified: Thu Mar 24 22:59:09 2011, max compression
#cp 3 3z.gz
#gunzip 3z.gz
gzip: 3z.gz: decompression OK, trailing garbage ignored
#file 3z
3z: Minix filesystem, 30 char names

As we can see the file '3' was a compressed Minix file system. Lets mount it and take a look around.

#mkdir cameraFS
#sudo mount -o loop -t minix 3z cameraFS/
#cd cameraFS/
#ls
bin dev etc lib linuxrc mnt proc sbin server tmp usr var

There is all sorts of interesting stuff in the "/server" directory but we are going to zero in on a specific directory "/server/cgi-bin/anony/"

#cd server/cgi-bin/anony/
#ls
jpgview.htm mjpeg.cgi mjpg.cgi view2.cgi

The "cgi-bin" directory is mapped to the root directory of http server of the camera, knowing this we can make a request to http://192.168.1.17/anony/mjpg.cgi and surprisingly we get a live stream from the camera.

video stream. giving no fucks.

Now at first I am thinking, well the directory is named "anony" that means anonymous so this must be something that is enabled in the settings that we can disable.... Looking at the configuration screen you can see where users can be configured to access the camera. The following screen shows the users I have configured (user, guest)

Users configured with passwords.

Still after setting up users with passwords the camera is more than happy to let me view its video stream by making our previous request. There does not appear to be a way to disable access to the video stream, I can't really believe this is something that is intended by the manufacturer. Lets see who is out there :)

Because the web server requires authentication to access it (normally) we can use this information to fingerprint the camera easily. We can use the realm of 'netcam' to conduct our searches

HTTP Auth with 'netcam' realm

Hopping on over to Shodan (http://www.shodanhq.com) we can search for 'netcam' and see if there is anyone out there for us to watch

9,500 results

If we check a few we can see this is limited to only those results with the realm of 'netcam' and not 'Netcam'

creepy hole in the wall

front doors to some business

Doing this manually is boring and tedious, wouldn't it be great if we could automagically walk through all 9,500 results and log the 'good' hosts.... http://consolecowboys.org/scripts/camscan.py

This python script requires the shodan api libs http://docs.shodanhq.com/ and an API key. It will crawl the shodan results and check if the device is vulnerable and log it. The only caveat here is that the shodan api.py file needs to be edited to allow for including result page offsets. I have highlighted the required changes below.

def search(self, query,page=1):
"""Search the SHODAN database.

Arguments:
query -- search query; identical syntax to the website
page -- page number of results

Returns:
A dictionary with 3 main items: matches, countries and total.
Visit the website for more detailed information.

"""
return self._request('search', {'q': query,'page':page})

Last I ran this there was something like 350 vulnerable devices that were available via shodan. Enjoy.

Update: We are in no way associated with the @TRENDnetExposed twitter account.

miércoles, 20 de mayo de 2020

How To Spoof PDF Signatures

One year ago, we received a contract as a PDF file. It was digitally signed. We looked at the document - ignoring the "certificate is not trusted" warning shown by the viewer - and asked ourselfs:

"How do PDF signatures exactly work?"

We are quite familiar with the security of message formats like XML and JSON. But nobody had an idea, how PDFs really work. So we started our research journey.

Today, we are happy to announce our results. In this blog post, we give an overview how PDF signatures work and on top, we reveal three novel attack classes for spoofing a digitally signed PDF document. We present our evaluation of 22 different PDF viewers and show 21 of them to be vulnerable. We additionally evaluated 8 online validation services and found 6 to be vulnerable.

In cooperation with the BSI-CERT, we contacted all vendors, provided proof-of-concept exploits, and helped them to fix the issues and three generic CVEs for each attack class were issued: CVE-2018-16042, CVE-2018-18688, CVE-2018-18689.

Full results are available in the master thesis of Karsten Meyer zu Selhausen, in our security report, and on our website.

Digitally Signed PDFs? Who the Hell uses this?

Maybe you asked yourself, if signed PDFs are important and who uses them.
In fact, you may have already used them.
Have you ever opened an Invoice by companies such as Amazon, Sixt, or Decathlon?
These PDFs are digitally signed and protected against modifications.
In fact, PDF signatures are widely deployed in our world. In 2000, President Bill Clinton enacted a federal law facilitating the use of electronic and digital signatures in interstate and foreign commerce by ensuring the validity and legal effect of contracts. He approved the eSign Act by digitally signing it.
Since 2014, organizations delivering public digital services in an EU member state are required to support digitally signed documents, which are even admissible as evidence in legal proceedings.
In Austria, every governmental authority digitally signs any official document [§19]. In addition, any new law is legally valid after its announcement within a digitally signed PDF.
Several countries like Brazil, Canada, the Russian Federation, and Japan also use and accept digitally signed documents.
According to Adobe Sign, the company processed 8 billion electronic and digital signatures in the 2017 alone.

Crash Course: PDF and PDF Signatures

To understand how to spoof PDF Signatures, we unfortunately need to explain the basics first. So here is a breef overview.

PDF files are ASCII files. You can use a common text editor to open them and read the source code.

PDF header. The header is the first line within a PDF and defines the interpreter version to be used. The provided example uses version PDF 1.7.

PDF body. The body defines the content of the PDF and contains text blocks, fonts, images, and metadata regarding the file itself. The main building blocks within the body are objects. Each object starts with an object number followed by a generation number. The generation number should be incremented if additional changes are made to the object.

In the given example, the Body contains four objects: Catalog, Pages, Page, and stream. The Catalog object is the root object of the PDF file. It defines the document structure and can additionally declare access permissions. The Catalog refers to a Pages object which defines the number of the pages and a reference to each Page object (e.g., text columns). The Page object contains information how to build a single page. In the given example, it only contains a single string object "Hello World!".

Xref table. The Xref table contains information about the position (byte offset) of all PDF objects within the file.

Trailer. After a PDF file is read into memory, it is processed from the end to the beginning. By this means, the Trailer is the first processed content of a PDF file. It contains references to the Catalog and the Xref table.

How do PDF Signatures work?

PDF Signatures rely on a feature of the PDF specification called incremental saving (also known as incremental update), allowing the modification of a PDF file without changing the previous content.

As you can see in the figure on the left side, the original document is the same document as the one described above. By signing the document, an incremental saving is applied and the following content is added: a new Catalog, a Signature object, a new Xref table referencing the new object(s), and a new Trailer. The new Catalog extends the old one by adding a reference to the Signature object. The Signature object (5 0 obj) contains information regarding the applied cryptographic algorithms for hashing and signing the document. It additionally includes a Contents parameter containing a hex-encoded PKCS7 blob, which holds the certificates as well as the signature value created with the private key corresponding to the public key stored in the certificate. The ByteRange parameter defines which bytes of the PDF file are used as the hash input for the signature calculation and defines 2 integer tuples:
a, b : Beginning at byte offset a, the following b bytes are used as the first input for the hash calculation. Typically, a 0 is used to indicate that the beginning of the file is used while a b is the byte offset where the PKCS#7 blob begins.
c, d : Typically, byte offset c is the end of the PKCS#7 blob, while c d points to the last byte range of the PDF file and is used as the second input to the hash calculation.

According to the specification, it is recommended to sign the whole file except for the PKCS#7 blob (located in the range between a b and c).

Attacks

During our research, we discovered three novel attack classes on PDF signatures:

Universal Signature Forgery (USF)
Incremental Saving Attack (ISA)
Signature Wrapping Attack (SWA)

In this blog post, we give an overview on the attacks without going into technical details. If you are more interested, just take a look at the sources we summarized for you here.

Universal Signature Forgery (USF)

The main idea of Universal Signature Forgery (USF) is to manipulate the meta information in the signature in such a way that the targeted viewer application opens the PDF file, finds the signature, but is unable to find all necessary data for its validation.

Instead of treating the missing information as an error, it shows that the contained signature is valid. For example, the attacker can manipulate the Contents or ByteRange values within the Signature object. The manipulation of these entries is reasoned by the fact that we either remove the signature value or the information stating which content is signed.
The attack seems trivial, but even very good implementations like Adobe Reader DC preventing all other attacks were susceptible against USF.

Incremental Saving Attack (ISA)

The Incremental Saving Attack (ISA) abuses a legitimate feature of the PDF specification, which allows to update a PDF file by appending the changes. The feature is used, for example, to store PDF annotations, or to add new pages while editing the file.

The main idea of the ISA is to use the same technique for changing elements, such as texts, or whole pages included in the signed PDF file to what the attacker desires.
In other words, an attacker can redefine the document's structure and content using the Body Updates part. The digital signature within the PDF file protects precisely the part of the file defined in the ByteRange. Since the incremental saving appends the Body Updates to the end of the file, it is not part of the defined ByteRange and thus not part of the signature's integrity protection. Summarized, the signature remains valid, while the Body Updates changed the displayed content.
This is not forbidden by the PDF specification, but the signature validation should indicate that the document has been altered after signing.

Signature Wrapping Attack (SWA)

Independently of the PDFs, the main idea behind Signature Wrapping Attacks is to force the verification logic to process different data than the application logic.

In PDF files, SWA targets the signature validation logic by relocating the originally signed content to a different position within the document and inserting new content at the allocated position. The starting point for the attack is the manipulation of the ByteRange value allowing to shift the signed content to different loctions within the file.

On a very technical level, the attacker uses a validly signed document (shown on the left side) and proceeds as follows:

Step 1 (optional): The attacker deletes the padded zero Bytes within the Contents parameter to increase the available space for injecting manipulated objects.
Step 2: The attacker defines a new /ByteRange [a b c* d] by manipulating the c value, which now points to the second signed part placed on a different position within the document.
Step 3: The attacker creates a new Xref table pointing to the new objects. It is essential that the byte offset of the newly inserted Xref table has the same byte offset as the previous Xref table. The position is not changeable since it is refer- enced by the signed Trailer. For this purpose, the attacker can add a padding block (e.g., using whitespaces) before the new Xref table to fill the unused space.
Step 4: The attacker injects malicious objects which are not protected by the signature. There are different injection points for these objects. They can be placed before or after the malicious Xref table. If Step 1 is not executed, it is only possible to place them after the malicious Xref table.
Step 5 (optional): Some PDF viewers need a Trailer after the manipulated Xref table, otherwise they cannot open the PDF file or detect the manipulation and display a warning message. Copying the last Trailer is sufficient to bypass this limitation.
Step 6: The attacker moves the signed content defined by c and d at byte offset c*. Optionally, the moved content can be encapsulated within a stream object. Noteworthy is the fact that the manipulated PDF file does not end with %%EOF after the endstream. The reason why some validators throw a warning that the file was manipulated after signing is because of an %%EOF after the signed one. To bypass this requirement, the PDF file is not correctly closed. However, it will be still processed by any viewer.

Evaluation

In our evaluation, we searched for desktop applications validating digitally signed PDF files. We analyzed the security of their signature validation process against our 3 attack classes. The 22 applications fulfill these requirements. We evaluated the latest versions of the applications on all supported platforms (Windows, MacOS, and Linux).

Authors of this Post

Vladislav Mladenov
Christian Mainka
Karsten Meyer zu Selhausen
Martin Grothe
Jörg Schwenk

Acknowledgements

Many thanks to the CERT-Bund team for the great support during the responsible disclosure.
We also want to acknowledge the teams which reacted to our report and fixed the vulnerable implementations.