URSNIF: The Multifaceted Malware

The URSNIF malware family is primarily known for being a data-stealing  malware, but it’s also known for acquiring a wide variety of behavior. Known URSNIF variants include backdoors (BKDR_URSNIF.SM), spyware (TSPY_URSNIF.YNJ), and file infectors (PE_URSNIF.A-O).

December 2014: Rise in URSNIF infections brought about by file infection routines

In December 2014 we discussed a rise in URSNIF infections, primarily in North America,  which were due to the addition of file infection to URSNIF’s routines.

The virus inserts the host file into its resource section, instead carrying out typical file infection routines like patching host files (via inserting malicious code). These variants targeted the following files:

February 2015: Another URSNIF outbreak seen

The February outbreak showed that the malware widened its scope and improved its stealth mechanism. The URSNIF variants are detected as PE_URSNIF.B-O and PE_URSNIF.B.

It uses strings already found in legitimate system files for its properties such as its file name, folder name, and registry entries. This is done to hide itself alongside other legitimate system files. The file names it uses are a combination of legitimate system file names; for example, the malware will name itself cmdlnsta.exe, a combination of legitimate file names cmdl32.exe and rwinsta.exe. URSNIF was known to exhibit this behavior before it became a file infector.

It also injects its code separately into each target process, perhaps to avoid memory scanners. We also noted that the hardcoded strings in this URSNIF wave are the same ones found in the December variants.

March 2015: URSNIF variants seen infecting more file types

URSNIF variants seen this month (PE_URSNIF.E-O and PE_URSNIF.E) have further widened their scope. This new wave now infects more file types, including Microsoft Office documents, spreadsheets, and presentation files. It uses strings from system files (as the earlier variants did), and uses existing folder names to name the dropped files in order to trick fool users into running them. This technique was not particularly effective, as it did not hide the original folder.

The table below compares the recent URSNIF variants:

Pre-file infector December 2014 February 2015 March 2015
Infected files None *.PDT, *.MSI, *SETUP*.EXE *.PDF, *.MSI, *.EXE *.PDF, *.MSI, *.EXE, *.PPT, *.PPTX, *.DOC, *.DOCX, *.XLS, *.XLSX
Name used in removable drive propagation None Temp.exe Temp.exe {Folder Name}.exe
Use random strings for file names? Yes No Yes Yes
Inject routines separately? No No Yes No
Polymorphic? No Yes Yes Yes

URSNIF’s known hooking functions

URSNIF is traditionally also known for hooking various executable files in order to monitor browsers. It hooks WS2_32.DLL and KERNEL32.DLL or CHROME.DLL to monitor Google Chrome, NSS3.DLL and NSPR4.DLL to monitor Mozilla Firefox, and WININET.DLL to monitor Internet Explorer. It also monitors other browsers like Opera and Safari.

Recent URSNIF variants have significantly modified the exact system APIs that it’s been hooking for years. Hooking these APIs allows the malware to perform a wide variety of information theft, such as taking screenshots, by intercepting the data contained in various normal commands. Together with the hooked APIs, this allows for powerful information theft capabilities. The list of hooked APIs is below.

2012-2013 2013-2014 2014-2015
InternetReadFile InternetReadFile HttpOpenRequestA
InternetReadFileExA InternetReadFileExA HttpOpenRequestW
InternetReadFileExW InternetReadFileExW HttpSendRequestA
HttpSendRequestA HttpSendRequestA HttpSendRequestW
HttpSendRequestW HttpSendRequestW HttpQueryInfoA
HttpOpenRequestA HttpQueryInfoA HttpQueryInfoW
HttpOpenRequestW HttpQueryInfoW InternetReadFile
InternetConnectA HttpAddRequestHeadersA InternetReadFileExA
InternetConnectW HttpAddRequestHeadersW InternetReadFileExW
InternetQueryDataAvailable InternetConnectA InternetQueryDataAvailable
InternetConnectW PR_Read
InternetQueryDataAvailable PR_Write
PR_Read PR_Close
PR_Write PR_Poll
PR_Close PR_Available
WSARecv LoadLibraryA
WSASend LoadLibraryW
Closesocket LoadLibraryExA
LoadLibraryExW LoadLibraryExW

URSNIF has been constantly evolving in recent months, showing multiple faces of itself and displaying a wide variety of behavior. It shows no clear signs of dying down, which means that the malware will continue to pose risks to users across various segments.

Post from: Trendlabs Security Intelligence Blog – by Trend Micro

URSNIF: The Multifaceted Malware

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Story added 27. March 2015, content source with full text you can find at link above.