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WeepSteel Malware Deployed via Sitecore Zero-Day Exploit

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4 unique sources, 4 articles

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Threat actors have exploited a zero-day vulnerability in Sitecore Experience Manager (XM) and Experience Platform (XP) to deliver WeepSteel malware. The flaw, tracked as CVE-2025-53690, affects versions prior to 9.0 and was exploited using a sample machine key from outdated deployment guides. The attack involved ViewState deserialization, internal reconnaissance, and the deployment of various open-source tools for persistence and lateral movement. The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has ordered federal agencies to patch the vulnerability by September 25, 2025. The vulnerability has a CVSS score of 9.0, indicating critical severity. The vulnerability was addressed by Sitecore, which has provided mitigation guidance and indicators of compromise (IoCs). The attacks were quickly disrupted, but they highlight the risks associated with using default or outdated configuration settings in web applications. The WeepSteel malware, a .NET assembly, enables the harvesting of system, network, and user information, which is then encrypted and exfiltrated to the attackers. The attackers also performed extensive reconnaissance and established multiple methods of persistence, including creating local administrator accounts and using Remote Desktop Protocol (RDP) for access. The flaw is not a bug in ASP.NET itself, but a misconfiguration vulnerability created by reusing publicly documented keys that were never meant for production. The attackers targeted the '/sitecore/blocked.aspx' endpoint, which contains an unauthenticated ViewState field, and achieved RCE under the IIS NETWORK SERVICE account. The malicious payload dropped was WeepSteel, a reconnaissance backdoor that gathers system, process, disk, and network information, disguising its exfiltration as standard ViewState responses. The attackers executed reconnaissance commands including whoami, hostname, tasklist, ipconfig /all, and netstat -ano. They also deployed Earthworm (a network tunneling and reverse SOCKS proxy), Dwagent (a remote access tool), and 7-Zip (for creating archives of stolen data). The attackers escalated privileges by creating local administrator accounts ('asp$', 'sawadmin'), cached credentials dumping, and attempted token impersonating via GoTokenTheft. Persistence was secured by disabling password expiration for these accounts, giving them RDP access, and registering Dwagent as a SYSTEM service. CVE-2025-53690 impacts Sitecore Experience Manager (XM), Experience Platform (XP), Experience Commerce (XC), and Managed Cloud, up to version 9.0, when deployed using the sample ASP.NET machine key included in pre-2017 documentation. XM Cloud, Content Hub, CDP, Personalize, OrderCloud, Storefront, Send, Discover, Search, and Commerce Server are not impacted. Sitecore published a security bulletin in coordination with Mandiant's report, warning that multi-instance deployments with static machine keys are also at risk. The recommended actions for potentially impacted administrators are to immediately replace all static <machineKey> values in web.config with new, unique keys, and ensure the <machineKey> element inside web.config is encrypted. It is recommended to adopt regular static machine key rotation as an ongoing security measure. The exploitation of CVE-2025-53690 is part of a broader trend of ViewState attacks this year, including vulnerabilities in Gladinet's CentreStack, ConnectWise, and Microsoft SharePoint Server.

Timeline

  1. 04.09.2025 11:46 4 articles · 25d ago

    WeepSteel Malware Deployed via Sitecore Zero-Day Exploit

    The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has ordered federal agencies to patch the Sitecore vulnerability by September 25, 2025. The vulnerability, CVE-2025-53690, has a CVSS score of 9.0, indicating critical severity. The attack chain documented by Mandiant involves the deployment of a combination of open-source and custom tools for reconnaissance, remote access, and Active Directory reconnaissance. The malware WEEPSTEEL borrows some of its functionality from an open-source Python tool named ExchangeCmdPy.py. The attackers have been observed using additional tools such as SharpHound and GoTokenTheft for various malicious activities. Sitecore has confirmed that new deployments now generate keys automatically and that all affected customers have been contacted.

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