BlackMatter: New Data Exfiltration Tool Used in Attacks

This is the third time a custom data exfiltration tool appears to have been developed by ransomware operators, following the earlier discovery of the Ryuk Stealer tool and StealBit, which is linked to the LockBit ransomware operation.

Exmatter is compiled as a .NET executable and obfuscated.
When run, it checks its command line arguments for the following strings: “nownd” and “-nownd”.
If either is found, it attempts to hide its own window by calling the “ShowWindow” API as follows:
ShowWindow(Process.GetCurrentProcess().MainWindowHandle, 0);

In order to identify files for exfiltration, it will retrieve the drive names of all logical drives on the infected computer and collect all file path names, disregarding anything under the following directories:
C:Documents and Settings
C:Program FilesWindows Defender Advanced Threat ProtectionClassificationConfiguration
C:Program FilesWindowsApps
C:ProgramDataApplication Data
C:ProgramDataStart Menu
C:System Volume Information
C:UsersAll Users

It will also exclude files of less than 1,024 bytes in size and files with the following attributes:

It will only exfiltrate files with the following extensions:

It attempts to prioritize files for exfiltration by using LastWriteTime.

Files that match the criteria are then uploaded to a remote SFTP server using the following parameters:
Host: 165.22.84[.]147
Port: 22

Exmatter also includes SOCKS5 configuration, but this is not used:
Host: 10.26.16[.]181
Port: 1080

When it has finished exfiltrating data, Exmatter starts the following process to remove any trace of itself:
Filename: “powershell.exe”
-WindowStyle Hidden -C $path = ‘[FILEPATH_OF_THE_EXECUTING_SAMPLE]’;Get-Process | Where-Object {$_.Path -like $path} | Stop-Process -Force;[byte[]]$arr = new-object byte[] 65536;Set-Content -Path $path -Value $arr;Remove-Item -Path $path;

This will attempt to overwrite an initial chunk of the file before deleting it.

Multiple variants of Exmatter have been found, suggesting that the attackers have continued to refine the tool in order to expedite exfiltration of a sufficient volume of high value data in as short a time as possible.

In a second variant, the directory “C:Program FilesWindows Defender Advanced Threat ProtectionClassificationConfiguration” has been replaced with “C:Program FilesWindows Defender Advanced Threat Protection” on the exclusion list.
The file types “.xlsm”, and “.zip” were added to the inclusion list.

A third version of note added a WebDav client.
The code structure suggests that SFTP remains the first choice protocol, with WebDav acting as a backup.

The WebDav client uses the following URL:

The following file types were also added to the inclusion list:

In addition to this, Exmatter is configured to skip exfiltration for files with names containing any of the following strings:
Adobe Sign

A fourth variant contained updated SFTP server details:
Host: 159.89.128[.]13
Port: 22

The WebDav client used the following updated URL:
Finally, the list of files for inclusion was updated by removing “.png”.

BlackMatter is linked to the Coreid cyber crime group, which was previously responsible for the Darkside ransomware.
For the past 12 months, it has been one of the most prolific targeted ransomware operators and its tools have been used in a number of ambitious attacks, most notably the May 2021 Darkside attack on Colonial Pipeline that disrupted fuel supplies to the East Coast of the U.S.

Coreid operates under a RaaS model, working with affiliates to conduct ransomware attacks and then taking a share of the profits.
Like most ransomware actors, attacks linked to Coreid steal victims’ data and the group then threatens to publish it to further pressure victims into paying the ransom demand.
Whether Exmatter is the creation of Coreid itself or one of its affiliates remains to be seen, but its development suggests that data theft and extortion continues to be a core focus of the group.

Sign Up For Threat Alerts

Threats Icon

Jan 29, 2023

APT15 Targets Multiple Sectors With Turian Backdoor

APT15, also known as Playful Taurus, is an advanced persistent threat (APT) that conducts a...

Threats Icon

Jan 26, 2023

Vice Society Ransomware Group Targets Manufacturing Companies

The Vice Society threat group was discovered targeting multiple sectors including manufacturing companies in Brazil....

Threats Icon

Jan 26, 2023

US Cert Alert – Alert (AA23-025A) Protecting...

Although this campaign appears financially motivated, the authoring organizations assess it could lead to additional...

Threats Icon

Jan 25, 2023

Emotet Malware Makes a Comeback with New...

The Emotet malware operation has continued to refine its tactics in an effort to fly...

Threats Icon

Jan 25, 2023


The DragonSpark attacks represent the first concrete malicious activity where Analysts observe the consistent use...

Threats Icon

Jan 25, 2023

PLAY Ransomware

PLAY is simple but heavily obfuscated with a lot of unique tricks that have not...

Threats Icon

Jan 24, 2023

Gamaredon Abuses Telegram To Target Ukrainian Government...

The Gamaredon APT group was discovered targeting Ukrainian government entities using the Telegram messaging service...

Threats Icon

Jan 23, 2023

NeedleDropper: A New Dropper-as-a-Service Uncovered

Avast's Threat Research Team has since October 2022 been observing a new strain of dropper...

Threats Icon

Jan 22, 2023

Aurora Stealer Leverages Shapeshifting Tactics And Popular...

A threat actor was discovered mimicking legitimate websites to host and deliver the 9002 RAT,...

Threats Icon

Jan 19, 2023

Earth Bogle Campaign Targets Entities With Geopolitical...

Middle Eastern geopolitical themed lures were used to distribute njRAT across the Middle East and...

Threats Icon

Jan 18, 2023

The NoName057(16) Hacktivist Group Targets Ukraine Supporters...

The NoName057(16) hacktivist group targeted multiple sectors across Ukraine and neighboring countries with DDoS attacks....

Threats Icon

Jan 17, 2023

Italy Targeted By Information Stealer Malware

An un-named information stealer was targeting end users in Italy through a phishing campaign using...

Threats Icon

Jan 15, 2023

The Australian healthcare industry was targeted by...

The Australian healthcare industry was targeted by the Gootkit loader malware; initial access was gained...

Threats Icon

Jan 11, 2023

Shc Linux Malware Used To Install XMRig...

External facing Linux servers in South Korea were targeted with a Shc (Shell Script Compiler)...

Threats Icon

Jan 11, 2023

Dridex Returns To Target MacOS With Updated...

Threat actors have been seen targeting Mac users with the Dridex malware. Although the malware...