Virustotal - Part 01
Introduction
VirusTotal is a website that scans files, webpages, domains, and IPs, against a large number of antivirus scanners. This allows a user to get feedback from a large number of sources and helps them determine if something is known to be malicious or known to be benign.
Files and URLs can be uploaded to VirusTotal. However, once they are uploaded, they should be considered public. Organizations that pay for access can download uploaded files. As a result, do not upload sensitive files or files that belong to your employer.
Virustotal Section Information
First File Hash
It is common for analysts to use VirusTotal to inspect malicious files, but it is also critical for recognizing benign files.
At VirusTotal, perform a lookup for the following filehash by
selecting Search and entering the hash 60517f898bfac156cd298fd0a45f2e06cecee232a54667213458b99dc8d80de7 and pressing enter.
In the header, VirusTotal provides a summary about the file.
In the top left, is a detection ratio: the number is the number of detections as malicious out of the total number of detection engines.
The header also contains the SHA256 hash of the file and a name for the file. This name may be the original name, internal name of the file, or the name may be the name of the first file with this hash that was uploaded. As a result, the name here may differ from the name of the file that was uploaded.
VirusTotal will also tag the file with key indicators below the file name.
One important tag to be familiar with is known-distributor. This tag is used for files that are provided to VirusTotal by a reliable source. During an investigation, if you start investigating a file with the known-distributor tag, there are a few possible scenarios:
Verifying the Correct File Hash: Sometimes, a legitimate program might be running or loading a malicious file. Security tools can sometimes mistakenly provide the hash (a unique identifier) of the legitimate program instead of the malicious file. To avoid this confusion, it’s important to double-check the file hash to ensure you’re analyzing the correct one.
Masquerading: Attackers often rename malicious files to make them look like legitimate ones. This technique, known as masquerading, helps them avoid detection by security tools that may be looking for specific process names. MITRE ATT&CK is a catalog of cyber attacks and has an entry for this technique.
DLL Search Order Hijacking: Sometimes, a legitimate file is used maliciously, such as in DLL Search Order Hijacking. This technique exploits the way programs search for DLLs (shared code libraries). By renaming a malicious file to match a benign DLL’s name, the attacker tricks the program into loading the malicious code instead of the legitimate one.
Supplier Compromise: Though rare, suppliers can be compromised and unknowingly distribute malicious files. For example, 3CX Desktop App is enterprise software that provides communications for its users including chat, video calls, and voice calls. In late March, 2023, a software supply chain compromise spread malware via a trojanized version of 3CX’s legitimate software that was available to download from their website
On the right side of the header, we see other details such as the file size, Last Modification Date, and file type.
The Last Modification Date refers to the last time the report was last updated. This matches the Last Analysis Date in another part of the report. You should always think of this date in the header as the last time the file was analyzed.
Users can manually trigger the file to be analyzed again by using the Reanalyze button above the last modification date.
Next to the Reanalyze button are two other buttons, Similar and More. Unfortunately, these options are not available to us with a free account. These options require subscriptions and cost a boat-load of money. However, we won’t let that stop us from learning. We’ll keep on analyzing.
Reanalyzing files is important in two situations:
First, the file appears to be old. Perhaps the file was uploaded to VirusTotal several years ago and the last analysis was also years ago. Reanalyzing the file will process the file again against new detections that may have become available since the time that the file was previously analyzed.
Second, the file may be very new. It is common with emerging threats that detections may not exist and VirusTotal may present the user with a low score (less than 10 detections) or even a clean score (0 detections). Reanalyzing the file will check the file against the detection engines again.
Let’s move over to the Details tab
In the Details tab, under the History section, you can see the Last Analysis date.
The First Submission date is for when the file was first uploaded to VirusTotal.
The Creation time is based on the file’s metadata.
Malware developers can change this date and sometimes, a weird date can be a suspicious indicator, but not always. Some types of files even default to having a certain date. In this case, the date is later than the first seen date, which is weird, but everything else with this file checks out as OK.
No one really knows what the First seen in the Wild date means. VirusTotal doesn’t explain it anywhere and the timestamp doesn’t make sense consistently. Don’t put much trust into it.
The last analysis date here is useful as it helps us know how long ago the file has been analyzed in contrast to the first submission.
The Last Submission date indicates the last time the file was uploaded.If something is new and being seen by many people, you can see the Last Submission get updated each time you refresh.
Another indication of users uploading the same file is the Names section, which is just below the History section.
The Names are the names of the files that have been uploaded.
Why might someone have uploaded a legitimate file with a wacky name like that?
As you may have concluded already, changing the name of a file doesn’t affect its file hash. The file hash will stay the same no matter what the file is named.
In this case, the list of Names is pretty long. rundll32 commonly gets abused, so it is important to be careful: that is, you don’t want to set security tools to block or alert a file named rKpPlCbFgHgAfYwYlYjWu just to find out that you blocked a legitimate Windows application! Blocking a legitimate file could cause an outage for users or for a whole enterprise.
Above the History section is a Basic Properties section. This section contains a variety of file hash types. If you ever need an MD5 or SHA-1 hash, this is a good place to find it. The other hashes may become useful to you as you get familiar with other hash types.
This section also provides more detail on the file type. This can be useful if the file type isn’t completely clear or if you need to know more nuanced detail about the file type.
Below the Names section, there is an optional Signature Info section.
Developers can digitally sign files as evidence the file came from them. The signature contains a hash of the file so that if the file is modified in any way, the signature will flag as Invalid indicating that the file has been tampered with.
Microsoft often signs their files, but not always. As a result, the signature can be an unreliable source of truth as to if the file is from Microsoft or not.
In order to sign a file, a company needs to “prove” to a certificate issuer that they are a legitimate company.
This system can be abused, so it is important to take a look at the company in the certificate and determine if it makes sense with everything else you know about the file.
The file is then signed by the developer and then signed by the certificate issuer. The developer’s name is usually listed first.
Take a look at the first signer of the file with the hash: 4788925332fc6128c895b0e0736a1d7d90e3891f2abb456523cbf0c1ced7d1e2
(Search for that hash, and look in the Details tab)
In the Signature Info section, the File Version Information is extracted from the file itself. The copyright, product, description, original name, and other details are all controlled by the creator of the file. Since they are controlled by the creator, they should only be trusted if you trust the file.
Look at the File version information for the following file: 549ff37e56d372d076a3d11cd33af660568dc1048b1f4ecce77d8b334582c6c8
At the time of this writing, the last time the file was analyzed was a year ago, and the certificate appears valid. The file only had 2/70 detections. According to the file, the copyright belongs to Intel Corporation.
But this file first signer is M-Trans Maciej Caban
Second File Hash
I found a sample with the same Certificate signer as in above file.
The file hash is a50bcbf0ef744f6b7780685cfd2f41a13be4c921d4b401384efd85c6109d7c00, however, it has a lot more hits by detection engines!
Let’s look at the Detections tab.
There are a few sections of this page that are only visible if you are logged in. These sections are Crowdsourced YARA rules and Crowdsourced Sigma Rules. It is beyond the purpose of this lesson to discuss YARA rules and Sigma rules, but the important thing right now is knowing that VirusTotal users can contribute custom rules. You are also able to view these rules by hovering over the rule and clicking View Ruleset. This is useful if you want to understand why the rule fired or if you want to use the rule elsewhere.
The largest section on the page is the Security vendors’ analysis. This section shows the results from many different security vendors. The number of vendors who detected something malicious contributes to the detection ratio in the header.
Newer analysts can sometimes make a mistake of assuming something is malicious because it has some detections, but it is good to understand who is detecting what. No vendor is perfect, but there are definitely some vendors who are more reliable and well known than others.
Sometimes, directly above this section, there is a bar that summarizes some of the detections. This includes a Popular threat label and a summary of tags.
That label suggests the file is a Trojan and Stealer (also known as Information Stealing malware) which may steal passwords from the computer and browser. The community tab can often help us learn more.
Let’s go to the community tab. Make sure you are logged into your account. You will see a section called Contained in Collections.
VirusTotal allows users to group common files and indicators together in a collection. According to this page, numerous users have a collection that contains this file. By looking at these collections, or the information associated with them, we can learn more about the file.
Example below:
The Comments section contains information submitted by registered users and can often help an investigation substantially. We can use information we find here and see if it matches the behavior in our investigation.
Let’s look at a new file: the file hash is a54ca708c3bbef76dbaec817a9bb36d8b52e492b293d2127cd5be284caabb6d1
The file has a low detection ratio: 7/62 at the time of this writing.
This ratio may change as more vendors either scan or detect this file
Just looking at the numbers, this ratio is inconclusive as to whether the file is malicious or not. However, if we look at the Community tab and the Comments section, we see a helpful comment from colinc_sophos.
Be careful: threat actors leave comments too!
Previously, this malware had a comment from a threat actor stating that it was Clean! The threat actor has now been banned from VirusTotal and their comments removed.
In that situation, colinc left robust comments on all the same files that the threat actor had commented on. colinc was able to do this because you can see all of someone’s comments by clicking on their profile image.
Looking at someone’s profile can help you understand how reliable someone is and it may also help you find related malware.
After clicking on their image, the profile header has their username and their name.
This file has a low score because of anti-analysis techniques and because it can no longer retrieve its malicious payloads. As a result, most of the behavior is unavailable to the sandboxes and from the detection engines.
As a result, comments like ones left by colinc_sophos can help provide context that VirusTotal itself does not provide.
When you analyze files in the future, consider leaving comments for others who may investigate the same file as you. You can also vote using the Community Score buttons under the detection ratio. The ❌ will downvote, and the ✔️ will upvote.
The ✔️ vote in the VirusTotal vote section indicates that a user believes the file, URL, or IP address is safe or benign. It’s a way for users to collectively contribute their assessments, helping others to determine the safety of a given item.
The ❌ vote in the VirusTotal vote section indicates that a user believes the file, URL, or IP address is malicious or harmful. This helps the community by signaling potential threats and contributing to the collective understanding of the item’s safety.
MITRE ATT&CK describes the technique from the above file:
T1583.008: Adversaries may purchase online advertisements that can be abused to distribute malware to victims. Ads can be purchased to plant as well as favorably position artifacts in specific locations online, such as prominently placed within search engine results. These ads may make it more difficult for users to distinguish between actual search results and advertisements. Purchased ads may also target specific audiences using the advertising network’s capabilities, potentially further taking advantage of the trust inherently given to search engines and popular websites.
Deep dive on VT
Third file Hash
Let’s take a look at this file, the hash is at0221bf1e1bd171c17527a863531518a95bcc025c87888e66b9512a5651073d16.
Oh dear! This file has even more detections than the last one.
Based on the header, someone appears to have uploaded the file with a name that includes the file hash.
Let’s look at the Relations tab. In this tab, we will see information such as what domains and IP addresses a file connects to.
According to the relations tab, plivetrakoy.com domain was contacted by this file
The Relations tab is a great place to pivot on suspicious indicators.
To “pivot” is to take an indicator and use it to turn in a new direction. This can help find new indicators and can help find related files. To pivot on the domain, click the above domain that you found. Clicking the domain will navigate to the VirusTotal page for that domain.
Up until this point, we have only looked at file analysis in VirusTotal, but VirusTotal also has analysis for domains and IP addressess.
The Details page is consistent with what you might expect for a domain, such details about as DNS Records. We will not dig into these details for this lesson, but it is good to know they are here
If we look at the Relations tab, we can see a section called Passive DNS Replication. These are the IP addresses that had resolved to the suspicious domain.
The IP address resolved to this domain on the date closest to when the file was submitted to VirusTotal is 193.149.180.175
File submitted date,
Pivoting gives you as an analyst more information to search on. You can also leverage this information to identify if hosts in the environment have indicators you found whie pivoting. Originally, we only had a filehash, but now we have a filehash, a domain, and an IP address.
While on the VirusTotal page for the domain, we can look at the Communicating Files section on the Relations tab. This section can be useful when you don’t know if an IP address being used maliciously or not.
Let’s return to the previous file. We can do this by clicking the filename in the Communicating Files section or by searching for the file hash 0221bf1e1bd171c17527a863531518a95bcc025c87888e66b9512a5651073d16 again.
Returning to the Relations tab:
We also see a section called Execution Parents. This section exists when a file was dropped by another during analysis. This can give us some clues as to where the file came from. In this case, it looks like it came from a ZIP file.
If we click the file name of the execution parent, we can pivot to that file. This file is a ZIP file.
Any ZIP file uploaded to VirusTotal will be extracted and the contents will be submitted for their own analysis. This is important to know in case other files in the ZIP are necessary for the malicious file to execute. That is not the case in this situation: it appears the ZIP file only has 1 file inside of it based off of the Relations tab.
Fourth file Hash
I found a sample with the same Certificate signer as in above file.
The file hash is 2bf0a64fe7aea262c96fc7d52b1e28486ff607caa9513fd88583e19454f9c500
We will now look at the Behavior tab to understand what this file does.
At the top of the Behavior tab, it will list any sandboxes that were used to analyze the file. The only sandbox in this instance is DrWeb vxCube.
There are often more sandbox reports, but there may only be one sandbox due to the file’s large size. Many sandboxes cannot handle sizes larger than 100MB and the maximum size that can be uploaded to VirusTotal is 650MB.
Attackers are aware of these size limitations and pump or inflate their files to be too large for sandbox analysis.
Defenders can defeat this technique by deflating the file. One tool that does this is called Debloat.
A deflated copy of this file was uploaded to VirusTotal: 71d5a558096b640366dbc711ef2870c0269b4138352bb98da0be30d9b6d6bb9b When uploaded, it was able to be analyzed with 5 sandboxes this time.
Let’s return to the inflated file and look back to the Behavior tab. When we look at the report, we can learn a lot about what the file did.
2bf0a64fe7aea262c96fc7d52b1e28486ff607caa9513fd88583e19454f9c500
File system actions records any files opened, written, or dropped by the file. During the analysis, a file was written in an important file path. Any file in this file path will be executed when the user logs onto the device.
Below the File system actions section is a section called Registry actions. On a Windows machine, the Registry is responsible for the device’s configuration and the Registry handles many aspects of the computer.
When this file executed, it modified some registry keys. Registry keys are separated into hives and the hive associated with the registry key is listed at the beginning of the key. The registry hive modified by the malware is abbreviated HKCU (HKEY_CURRENT_USER).
VirusTotal records what is written in the registry keys when they are modified. To view the contents, click the + to the left of the registry key.
One of the keys contains the path shell\open\command. Here, when this registry key is called, the malicious Powershell script will be executed.
Below the Registry actions section is a section called Process and service actions. One of the categories here is Process tree.
A Process tree shows the relation between executed files. If a process spawns another process, the first process is called a parent process and the second is called a child process.
Child Processes are indicated here with an arrow curving to the right.
I hope you have gained a good basic knowledge about Virustotal from this writeup. In the next writeup we will see how VT is used for Advanced Threat hunting. ✌