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New ‘GIFShell’ Attack Technique Exploits Microsoft Teams GIFs

A new ‘GIFShell” attack technique exploits bugs and vulnerabilities in Microsoft Teams to abuse legitimate Microsoft infrastructure, execute malicious files, execute commands, and exfiltrate data.

According to Bobby Rauch, the cybersecurity consultant and pentester who discovered the hidden vulnerabilities, the “GIFShell” technique allows attackers to create a reverse shell that transmits malicious commands via base64 encoded GIFs in Teams. The outputs are then exfiltrated through GIFs retrieved by Microsoft’s own infrastructure.

To create the reverse shell, attackers need to convince a user to install a malicious stager that executes commands and uploads command output via a GIF URL to a Microsoft Teams web hook.

Microsoft Teams vulnerabilities exploited by the malware include Microsoft Teams security controls bypass which allows external users to send attachments to Microsoft Teams users.

The malware also modifies sent attachments to allow users to download files from an external URL instead of the generated SharePoint link. It forges attachments from Microsoft Teams to appear as harmless files, but instead downloads a malicious executable program or document. It uses insecure URLs to allow SMB NTLM hash theft or NTLM relay attacks.

Microsoft supports sending HTML-based 64-encoded GIFs, but does not scan the byte content of these GIFs. This allows malicious commands to be delivered within a normal-looking GIF. Since Microsoft stores Teams messages in a parsable file located locally on the victim’s machine, it can be accessed by a less privileged user.

Microsoft servers fetch GIFs from remote servers that allow data exfiltration via GIF file names.

The sources for this piece include an article in BleepingComputer.

New Ransomware hits Chile’s Windows and Linux servers

A ransomware attack that began on Thursday, August 25, involved Windows and Linux systems operated by the Chilean government agency, and the incident was verified by the Chilean computer security and incident response team (CSIRT).

According to Chile CSIRT, the hackers stopped all running virtual machines and encrypted their files while adding the “.crypt” filename extension. The authority explained that the malware has functions for various types of malicious activity, including stealing credentials from web browsers, the list of detachable devices for encryption, and evading antivirus detection by means of execution timeouts.

The ransomware attack is a double extortion attack. The attackers provided the Chilean CSIRT with a communication channel through which they could negotiate the payment of a ransom. This will help prevent the attackers from leaking the files and unlock the encrypted data.

The attackers set a deadline of three days and threatened to sell the stolen data to other cybercriminals on the dark web. While the Chilean CSIRT did not name the group behind the attack, the extension attached to the encrypted files indicated, however, that the malware pointed to ‘RedAlert’ ransomware. RedAlert ransomware used the ‘.encrpt’ extension in attacks that targeted both Windows servers and Linux-VMWare ESXi machines.

In his analysis of the malware, Chilean threat analyst Germán Fernández stated that the strain appears to be entirely new and that the researchers with whom he analyzed the malware could not link it to known families.

“One particular thing about the attack, is that the threat actors distributed the ransom note at a previous stage to the deployment of the ransomware as the final payload, possibly for evasion issues or to avoid having their contact details leaked when sharing the final sample,” Fernández said.

To protect against further attacks, Chile’s cybersecurity organization recommends a number of security measures to all government agencies and large private organizations. These include using a properly configured firewall and antivirus tool, updating VMware and Microsoft assets, securing key data, verifying the configuration of anti-spam filters, implementing network segmentation, and patching and mitigating new vulnerabilities.

The sources for this piece include an article in BleepingComputer.


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