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Malware Can Be Hidden in DICOM Medical Imaging Files, DHS Warns

Files using the Digital Imaging and Communications in Medicine (DICOM) standard can be abused to hide malware, the U.S. Department of Homeland Security (DHS) warned on Tuesday.

An alert issued by the DHS’s National Cybersecurity and Communications Integration Center (NCCIC) on the ICS-CERT website is based on a blog post published in mid-April by Cylera, a company that provides cybersecurity and intelligence solutions for healthcare organizations.

Cylera’s Markel Picado Ortiz discovered a “fundamental design flaw” in DICOM, a widely used international standard for storing, transmitting, retrieving, processing and displaying medical imaging information.

The organization that maintains the standard says DICOM is used in virtually all hospitals around the world, including by imaging equipment (CT, MR, ultrasound), imaging information systems (HIS, RIS, PACS), and peripheral equipment (workstations and 3D printers).

Ortiz discovered that a 128-byte section at the beginning of DICOM files, called a preamble, can be used to hide malicious executable code. The preamble is part of a compatibility feature designed to allow medical imagery files to be processed by both DICOM and non-DICOM software.

The resulting file stores both the legitimate medical information — this information can be accessed by the user as the modifications don’t corrupt the file — and the malware.

“By exploiting this design flaw attackers can take advantage of the abundance and centralization of DICOM imagery within healthcare organizations to increase stealth and more easily distribute their malware, setting the stage for potential evasion techniques and multi-stage attacks,” Cylera said. “Perhaps more interestingly, the fusion of fully-functioning executable malware with HIPAA-protected patient information adds regulatory complexities and clinical implications to automated malware protection and typical incident response processes in ways that did not previously need to be considered. Common incident response procedures could now delete or incidentally leak the ePHI the malware is hiding in.”

Cylera published technical details and proof-of-concept (PoC) code for this vulnerability, which has been assigned the CVE identifier CVE-2019-11687.

NCCIC noted in its advisory that it has notified some of the vendors using DICOM. The agency and the DICOM Security Group have identified a series of mitigations that organizations can use to mitigate the risk. NCCIC also highlighted that Cylera disclosed the flaw without coordinating with the agency or any known vendor.

The DICOM Security Group published a press release and a FAQ for this vulnerability last month.

“A malicious actor could modify a DICOM file so that it is treated as both an executable program and as a DICOM file, and then a user might be convinced to execute the file via social engineering,” DICOM said. “Alternatively, a separate malicious actor that knew about the embedded executable and had access to the modified file could install and execute the malware. This type of intrusion is referred to as a multi-phase attack.”

Recommendations for mitigating the risk include scanning DICOM files with antimalware software, being cautious with files from untrusted sources, and verifying the preamble to ensure it’s either cleared or safe.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.