Taiwan is a logical target since they have a history of accepting Tibetan refugees. Also, the other target is a professor at the Central University Of Tibetan Studies in India—a institution founded by the first Prime Minister of India with the Dalai Lama himself. It was established in 1967 to educate exiled Tibetans and to preserve Tibetan culture and history.
The attackers, called the “Shiqiang gang“, show a consistent modus operandi. They use similar remote administration tool (RAT) payloads, stolen certificates, and seem to target anyone pro-Tibetan. The RAT payload in this attack in called “GrayPigeon,” also known as ”Huigezi” in Chinese. It is very popular in the Chinese webspace which indicates that the attackers speak the language. The RAT payload has multiple layers of encryption making it harder to identify.
The threat arrives in the form of a targeted email with an XLS attachment. The content of the emails are as shown below in Figure 1 and Figure 2. The email attempts to draw on the sentiments of the Taiwanese government and activists towards the exiled members of the Tibetan government.
The content of both the emails are similar and roughly translate to:
To friends who care about the Tibetan government-in-exile
Now we publish this for you <<Tibetan government-in-exile offices in the Americas 2013 for the second half the year with detail list requesting for comments>>
Do not distribute this letter and this is only for friends who care about this
Also hope that you can actively participate in our activities in the second half of the year
Office of the Tibetan government-in-exile in the Americas
Chinese chief liaison officer Gongga Tashi kungatashi
Technical Analysis: How the Attack Works
The attached file in both emails is the same (2010790755b4aca0edc3c50ee8480c0b) When opened, the XLS file exploits CVE-2012-0158 and launches a decoy document as shown in Figure 3. The decoy document contains a ruse as usual and this time it states that Tibetan fonts are missing. In the background, it drops a series of files eventually leading to the launch and execution of 2013soft.dll. This in turn injects a RAT payload in to explorer.exe.
Analysis of Payload:
The main functionality lies within 2013soft.dll (28426ddc3c49635c11a2ee72118e9814) and the subsequent DLL it decrypts and injects in to explorer.exe (05eda4aaa49b2409f52cf2356f4a91db).
On inspection of 2013soft.dll, it is evident that this payload contains a rather large resource section. The MAIN stub in resource section holds large amount of data however it appears to be encrypted.
On dynamic analysis of the payload, it becomes clear that the Main stub eventually decrypts to the final DLL payload. The stub is loaded into memory and decrypted using the loop shown in Figure 5. It operates on 8 bytes of data at a time and uses the 16 bytes key “1234567890ABCDEF”. This, in addition to that fact that it uses the constant value 0x9E3779B9, gives away the algorithm as TEA (Tiny encryption algorithm). The TEA algorithm uses this value as the Delta constant.
It then jumps to the decrypted stub after setting the memory region it resides in as executable. The start of this decrypted MAIN stub contains an XOR decryption loop shown in Figure 6. This decryption loop decrypts the remainder of the stub. Notice how the XOR key “0x27691C” is only 3 bytes in length but the EAX pointer is incremented by 4. This means the first byte in every 4 bytes (little endian) is not subjected to XOR.
You would think we have the payload after two levels of decryption but not in this case. It jumps to another shellcode, which performs a rolling byte XOR decryption using a 4 byte key on the latter part of the stub.
Now we are getting somewhere as we can see an MZ file header interspersed with other characters past the “MinxxxA” marker as shown in Figure 8. This data is then subjected to what appears to be a custom decompression algorithm, following which it is injected into a new instance of explorer.exe
The injected DLL payload is a variant of the RAT called “GrayPigeon“ also known as “Huigezi” which is popular in the Chinese web space. It is written in Delphi and contains comprehensive functionality. The RAT uses various Pascal modules  such as “TscreenCaptureUnit.pas” and “UnitServices.pas” also widely seen on Chinese forums and associated with this RAT.
It creates a mutex “\BaseNamedObjects\windows!@#$” and sets up startup persistence by adding a registry key “\Software\ts\Explorer\run\2013Soft\run = rundll32.exe C:\WINDOWS\2013soft.dll,Player”. In this case the RAT was observed key logging and storing the data under C:\WINDOWS\2013soft.log along with the corresponding Window names.
It then uses the same TEA (Tiny Encryption algorithm) described earlier to decrypt the address of the command and control server “help.2012hi.hk”. It reuses the key “1234567890ABCDEF” for TEA decryption. It makes a DNS query specifically to Google’s DNS server 184.108.40.206 and it attempts to connect to the resolved server on port 91.
We observed the following outbound communication on port 91.
This GrayPigeon RAT instance we analyzed had extensive functionality and a summary of the features is listed below:
- Determine Host name and OS version
- Ability to log keystrokes and mouse events
- Ability to capture users screen
- Ability to use Telnet protocol
- Ability to send and receive files
- Sniff URL addresses from Internet Explorer and read form values
- Get list of active services
- Ability to shutdown/restart etc.
We mined for other samples talking to the same C&C infrastructure and we found two with the md5sums 4e454584403d5521abea98d21ee26f72 and 7de5485b7dd154a9bbd85e7d5fcdbdec which drop Hangame RAT and GrayPigeon RAT respectively. The RAT payloads in these instances also phone home to help.2012hi.hk. This C&C domain was also referenced in a white paper published by Symantec as part of the overall campaign coined the Elderwood project . The campaign in the current instance and related samples are more in line with Tibetan themed attacks on NGOs and Taiwanese officials. The campaign also heavily uses stolen certificates. These have been attributed with the Shiqiang gang as discussed by Snorre Fagerland from Norman and also discussed by Trend  and AlienVault .
The decoy document associated with 7de5485b7dd154a9bbd85e7d5fcdbdec also has a Taiwanese target as evident from the contents of the document.
Also, both these two variants interestingly have digital certificates in the payload . The certificate for 4e454584403d5521abea98d21ee26f72 is a stolen certificate that has already been revoked.
Version: 3 (0×2)
Signature Algorithm: sha1WithRSAEncryption
Not Before: Dec 8 00:00:00 2011 GMT
Not After : Dec 7 23:59:59 2012 GMT
Subject: C=CN, ST=Guangdong, L=Shenzhen, O=Shenzhen Xuri Weiye Technology Co., Ltd., OU=Digital ID Class 3 – Microsoft Software Validation v2, CN=Shenzhen Xuri Weiye Technology Co., Ltd.
The certificate for 7de5485b7dd154a9bbd85e7d5fcdbdec appears to be modified manually and is invalid.
Version: 3 (0×2)
Signature Algorithm: sha1WithRSAEncryption
Issuer: C=CN, ST=Beijing, L=Beijing, O=CA365, CN=CA365 Free Root Certificate
Not Before: Oct 23 10:47:29 2010 GMT
Not After : Oct 23 10:47:29 2011 GMT
Subject: C=CN, ST=shanghai, L=shanghai, O=International Test User, OU=Market, CN=International Test User