Try to add executive summaries so that the technical management has something to talk about from your technical analysis. Ideally, do some intelligence news gathering from online sources or any of your own and give reasons as to why you infer that the malware sample is malicious (MO?) and to what level. Give a few highlights and end with the mitigation measures as recommended by your team or as per your company guidelines. The following paragraph is a simple first draft of what you could possibly note down in a more generic manner related to the details you got out of this particular analysis session. You must also supplement your debrief using graphs and statistics if applicable.
This particular variant of the Dark Seoul malware is reported as Wiper A by some security vendors in a septet of seven samples collected till date, with six being wipers and one being a dropper. The other variants are dropped independently and their launchers have not yet been discovered.
The file is malicious and has been widely reported as an infection in South Korean Banks. As we see, structurally the file looks benign and is unobfuscated. However, the payloads and modus operandi are clear at this point. This MBR infector tries to end the Windows session after infection. It creates another process and injects its code in taskkill.exe. It uses this to search for antivirus services of popular Korean AV products—AnhLab and Hauri—and terminates them.
The binary initially contains only one import; however, we see that more imports are being dynamically loaded using PEB traversal.
Unreachable code is also executed as an internal table of function addresses are built and then referenced.
The file not being obfuscated structurally might have also made it pass obvious detection using entropy and compression/obfuscation as malicious indicators. It looks benign, but is in fact very malicious. It got detected because computers started rebooting and destroying the computer by overwriting the MBR, which is being detected as a payload.
Signatures can be taken from the various static offsets of the malware. We already have a plethora of unique strings and entire byte sequences that can be taken as hex signature. Yara signatures can be constructed (see in the next segment) and Snort signatures can be built for this malware if it is downloaded on the network as is without the dropper component (the dropper drops trojaned binaries and UPX packed files, so the inspection has to be deep or else false positives will be generated by the detection system). It does not have any network activity but it uses a launcher to spread and infect, which is distributed separately.
MBR can be repaired using various boot rescue disks. Every antivirus vendor provides one from their website and there are third-party and open source products as well. For Windows, always prepare a live rescue disk for your workstations so that the MBR can be repaired in situations like this.
Booting into a Linux Live CD distro will also allow you to use utilities such as GParted to reconstruct the MBR. You can also use a hex editor and manually reconstruct the affected areas.
Most antivirus products detect this malware and its various variants.
Some of the malware functions and in binary attributes are like templates and markers, which could be for future malware variants, and this can be useful for generic signatures.
At this point, your analysis is complete, and how you compile and present your report is dependent upon your requirements. You have the details, the screenshots, the analyses, and the collected information from the sandboxes and the web. You can proceed with the other samples from the collection and start writing 1:1 (one to one) or static signatures, and 1:X (one to many) or generic signatures and finding patterns of interest, something which will identify the whole malware family as the next step ideally.