Malware writers can trick you in 2 ways into thinking your file is a "PDF looking" file using the Right-to-Left embedded characters.
Firstly, a maliciously constructed “.exe” can be built to display an PDF icon, so it looks like PDF default reader will open this file. If the filename is really long then, you can't see the extension (see image below).
2ndly and may not be so obvious, malicious PDF filename is constructed as with a right-to-left override character is such a way that the file ends ".pdf" extension, but really is an ".exe". So in example below, the 2nd file looks like a ".txt" file, but is really a ".docx" file (the 1st file). The 1st file has been cleansed of the RTL Unicode character, and ends in ".docx".
The PDF file is actually an ".exe" file, but looks like it will open with default PDF reader.
Here's the same files as viewed from the command (cmd.exe) line. The box character represents the RTL character.Note: Detection of malicious file is never done by a filename alone, so a good antivirus will flag the contents of this file, for known signatures. BUT you can remove the annoying RTL character with the free tool below!
How is RTLO being abused by malware writers?In apps that support Unicode like Window Explorer, the right-to-left override malware method uses a RTL Unicode character, that will reverse the order of the characters that follow it. It's used mainly for Middle Eastern/Asian languages that you read right-to-left.
RTLO can be used to spoof fake extensions. To do this we need a hidden RTL Unicode character in the file name.
What is “Right-to-Left Override” RTLO?
The RTLO method is used to hide the true type of a file, so
it might trick you into open text file (.txt) which really is a Word file (.docx) with malicious malware. More recently this file could hide a .wav file.
Audio files such .wav file are being embedded with malware, is on the forefront of malware maliciousness. Read about that on my post
here.
The method exploits a feature built into Windows Explorer. Since Microsoft Windows does a great job of supporting different languages from around the world, some of those languages that are written from right-to-left (RTL).
Let’s say you want to use a right-to-left written language, like Hebrew or Arabic, on a site combined with a left-to-right written language like English or French. In this case, you would want bidirectional script support.
Bidirectional script support is the capability of a computer system to correctly display bi-directional text. In HTML we can use Unicode right-to-left marks and left-to-right marks to override the HTML bidirectional algorithm when it produces undesirable results:
left-to-right mark: (
U+200E) Unicode character
right-to-left mark: (
U+200F) Unicode character
Here's a tool I built to clean up Right-to-Left Mark (and many others) and Unicode Control Characters from your files. It's super fast, small and written in native C++.
Updated Thu 21-Apr-22 - new build, fixed many recursive issues
Download touchRTL.7z (you need https://www.7-zip.org/ to unpack). For personal use only. Will open this page on each run. Copy into c:\windows to use from cmd.exe.
License :
touchRTL.7z personal use only, for commercial use buy touchLTRPRO. Contact as validated today available for license request.
touchRTLPRO.7z, has flags to remove Unicode spaces and punctuations (math symbols, currency, open closing braces, and accent marks).
Just run this command and it will recursively rename filenames to remove those characters under the specified directory name. If directory name, contains spaces you need quotes.touchRTL -v -R -l -y "directory name"
Usage: touchRTL [-aclmpRuvxy] [-r REFFILE | -d DATETIME] PATH...
UNIX touch mimic, updates files access, modification and creation times of file(s) in PATH to the current time,
If PATH argument does not exist, creates corresponding new empty file or directory (using -y), unless -c or --n
Supports directory recursion and time stamping!
Supports Right-to-Left (RTL) character removal for files.
PATH argument can represent a filename(s) or directory. Double quote if it contains spaces. eg "c:\as is.txt"
-a, --access-time change only the file access time
-c, --no-create do not create any new files - If the file exists, touch will update the access time,
-l, --RTL remove Unicode control & format characters (esp. infamous right-to-left) from filena
-m, --modif-time change only the file modification time
-p, --pause-exit pause on exit (non-GNU extra)
-R, --recursive recursively touch files in specified directory and all subdirectories (non-GNU extra
-u, --unicntrl remove Unicode control characters only - https://www.fileformat.info/info/unicode/ca
-v, --verbose output the result of every file processed (non-GNU extra)
-x, --creation-time change only the file creation time (non-GNU extra)
-y, --directory specify directory, instead of default file
-r, --reference REFFILE use this file's times instead of current time
-s, --spaces (PRO edtn) remove Unicode spaces from filename
-!, --puncs (PRO edtn) remove Unicode punctuations & symbols (math & modifiers) from filename
-d, --date DATETIME use YYYY-MM-DDThh:mm:ss[.ms] instead of current time (non-GNU, does not parse string
accepted "2033-04-01T07:07:07", "2033-04-01 07:07:07"
-h, --help Display this help and exit.
--version Display version information and license information.
For personal use only. Commercial license required for business use and removes page open. See --version for al
Copyright © 2019-2022 M. Pahulje <metadataconsult@gmail.com> - https://http://metadataconsulting.blogspot.com/
