What you need to know about the Duqu threat
November 2011, Security Services & Risk Management, Information Security
According to researchers at Symantec Security Response, this new malicious program has been developed to steal the kind of information needed to mount another Stuxnet-like attack. Here are the latest details.
On 19 October 19, Symantec released its analysis of a new threat, called Duqu, that appears to be the precursor to a future, Stuxnet-like attack. Parts of Duqu are nearly identical to the Stuxnet worm, but its sole purpose is to gather intelligence that could be used to give attackers the insight they need to mount future attacks. Duqu is not widespread, but it is highly targeted at suppliers to industrial facilities.
In at least one targeted organisation, Symantec has confirmed that the installer file was a Microsoft Word document, which exploited a previously unknown kernel vulnerability that allows code execution. When the document was opened, malicious code executed and installed the main Duqu binaries. Microsoft is aware of the vulnerability, and is working on issuing a patch and an advisory.
Duqu was recovered from a limited group of organisations based in Europe and first analysed by the Laboratory of Cryptography and System Security in Budapest.
How it works
Where Stuxnet was designed to reprogram industrial control systems (hardware used to manage industrial environments such as power plants and oil refineries), attackers have used Duqu to install keystroke loggers to gather information from the infected computers.
Although Duqu uses some of the same source code as Stuxnet, its payload is not destructive. It is primarily a remote access Trojan that does not self-replicate in order to spread itself, which means it is not a worm. Two variants of the threat were initially recovered, although Symantec has since discovered additional variants.
Duqu consists of an installer, a driver file, a main DLL, and a configuration file. Like Stuxnet, Duqu masks itself as legitimate code using a driver file signed with a valid digital certificate. The certificate, which belongs to a company headquartered in Taipei, was revoked on 14 October.
Attacks using Duqu and its variants may have been going on since last December based on a review of file-compilation times, according to Symantec.
Duqu uses HTTP and HTTPS to communicate with two known command-and-control (C&C) servers that are both now inactive. Attackers were able to download additional executables through the C&C servers, including an infostealer that can perform actions such as enumerating the network, recording keystrokes and gathering system information. The information is logged to a lightly encrypted and compressed local file, which is then exported.
The threat uses a custom C&C protocol, primarily downloading or uploading what appear to be JPG files. However, in addition to transferring JPG files, other data is encrypted and sent out. Duqu is configured to run for 30 or 36 days, at which point it will automatically remove itself from a system.
So far, Duqu infections have been confirmed in at least six organisations in eight countries (France, the Netherlands, Switzerland, the Ukraine, India, Iran, Sudan, and Vietnam).
Protect your private keys
The investigation by Symantec researchers concluded that some of the files associated with Duqu were signed with a private key stolen from an organisation, whose systems appear to have been compromised. The private key was associated with the code-signing certificate issued to that customer.
While it is not known how this particular key was compromised, Symantec offers the following recommendations to better protect private keys:
Separate test signing and release signing. It is a best practice to set up a parallel code-signing infrastructure using test certificates generated by an internal test root certificate authority. This ensures that business-critical private certificates used to sign officially released software are not stored on insecure build systems used for routine R&D software development tasks, reducing the likelihood that they will be compromised.
Cryptographic hardware modules. Keys stored in software on general-purpose computers are susceptible to compromise. It is more secure, and a best practice, to store keys in secure, tamper-proof, cryptographic hardware devices.
Physical security. There is no security without physical security. If it is possible for an outsider, or a malicious insider, to gain access to code-signing keys, then all cryptography measures are for naught. Cameras, guards, fingerprint scanners, and additional measures are all appropriate to protect critical assets and should be taken seriously.
Stuxnet opened the door to malware having profound political and social ramifications. While there is still much to be learned from the complexity of this threat, Stuxnet has already changed the way researchers approach malware and view the security threat landscape. The story continues now with Duqu, a new threat whose goal is to gather the intelligence that attackers need to mount a future, Stuxnet-like attack.
For a comprehensive technical analysis of this latest threat, download the Symantec Security Response White Paper: W32.Duqu: The precursor to the next Stuxnet