Emails with seemingly harmless invoice attachments continue to be a major target for cyberattacks, especially when they are disguised as HTML files. When opened, such attachments can execute scripts and download malicious code without the user noticing anything suspicious.
Our analysts recently observed exactly such a case in the control center. An HTML invoice opened in Outlook and displayed in Tangro, the digital document processing solution in SAP/S/4HANA, triggered a heavily obfuscated PowerShell command line in the background. This was hidden by XOR transformation and Base64 encoding and contained clearly malicious functionality.
Subsequent analysis revealed a multi-stage attack chain (“staged payload”) in which the malicious code was gradually downloaded and executed. Temporary scripts were created, files were downloaded from suspicious domains, and commands were executed via wscript.exe. There were also clear indications of attempts to communicate with a command-and-control server.
If the attack had been successful, the HANA instance in particular would have been an attractive target for further compromises due to the CVE-2025-42957 security vulnerability. The incident impressively illustrates how sophisticated and dangerous manipulated HTML invoices can be – and how important consistent security monitoring is in all phases of document management.
Risks:
- Initial system compromise: Opening the HTML file allows malicious code to be executed directly on the end device. The attacker gains initial access to the corporate network or user accounts.
- Reloading additional malware (staged payload): The attack proceeds in several phases, starting inconspicuously and becoming increasingly dangerous. Reloaded modules can read passwords, encrypt data, or set up persistent access, among other things.
- Bypassing security mechanisms: Obfuscation (e.g., XOR, Base64) makes malicious code difficult for virus scanners to detect. Conventional email filters or endpoint protection solutions often fail to detect it.
- Data theft and espionage: Access to confidential business data, customer data, or financial information. Possible exfiltration to command-and-control servers.
- Misuse of internal systems (e.g., SAP/HANA): Particularly sensitive systems can be accessed via Tangro and SAP. Compromising HANA instances potentially allows access to critical business processes.
- Business interruption and production downtime: Malware can encrypt or sabotage systems. This can lead to downtime in accounting, procurement, or production.
- Financial and legal consequences: Costs for recovery, incident response, and possible ransom demands. Data breaches can result in fines under the GDPR.
- Loss of reputation and trust: Disclosure of a cyberattack can undermine the trust of customers, partners, and investors. Long-term image and market consequences are possible.
Customer-specific measures implemented
Thanks to a rapid response and close cooperation with the customer, it was possible to contain the spread of the malware. The BlueTeam control center emphasizes the importance of continuous monitoring, patch management, and proactive organizational and technical measures to ward off future threats at an early stage.
- Isolation: The affected system was immediately shut down and removed from the network.
- Forensics: Hard disk images created; volatile storage material ideally backed up before shutdown.
- Accounts & access: Passwords reset, suspicious accounts deactivated; AD password of the affected user changed; no privileged admin account affected. AD account recreated after completion of forensics.
- User communication: Affected users informed and made aware; suspicious email deleted and removed from central mailboxes to prevent further infections.
- Restoration: Computers reinstalled (clean image, patches, hardening). Email/traffic check: Email flows and mailboxes checked for further spread.
Our recommendations for action:
- Patch management: Check security updates for critical systems. SAP HANA instances in particular should be up to date.
- Further forensics: In-depth analysis of affected files, logs, and network traffic to determine origin and scope.
- Employee training: Raise awareness of phishing indicators and how to deal with suspicious attachments/links.
- Process optimization: Review and improve incident response processes, email gateway/Mimecast rules, alert and escalation paths, and patch and backup processes.
Tangro/SAP HANA — specific notes:
- Recommendation: Please check the patch statuses of the SAP HANA instances and the Tangro integration points (file handling, preview/rendering of HTML/PDF, access rights between Tangro and SAP) immediately.
- Reason: If the Tangro asset is successfully compromised, the underlying SAP HANA instance would be an attractive target for follow-up attacks due to the known vulnerability CVE-2025-42957.
- Concrete action: Ensure that SAP patches 3627998 and 3633838 are installed on the affected systems. Also check Tangro configurations for insecure default settings (e.g., automatic preview of active content) and restrict rights between the Tangro service account and SAP systems according to the principle of least privilege.
Conclusion
This incident clearly shows how precise and professional cyberattacks are today. An inconspicuous email was enough to trigger a sophisticated chain of attacks, disguised by veiled scripts, cleverly embedded in familiar workflows and systems such as Outlook and Tangro. At the same time, however, the incident also showed how crucial strong partnerships are. Thanks to smooth cooperation with the customer and our shared understanding as part of the IT organization, the threat was detected early and successfully contained. This combination of technical expertise, clear processes, and direct communication was the key to preventing worse consequences.
Because one thing is certain: Cybersecurity is not a product, but an attitude. It is achieved through continuous vigilance, state-of-the-art protection mechanisms, and a high level of security awareness at all levels.
“Attacks like this show how important it is to address both technical and human risks.” – Analyst at the Certified Security Operations Center Team.
Only those who strengthen both technology and people will stay one step ahead of attackers in the long term.