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Several Dutch hospitals temporarily took parts of their systems offline over the weekend, preventing patients from accessing their medical records, following warnings about a serious security flaw in widely used software. This was a precautionary measure, not the result of a cyberattack, and the issue has since been resolved.
What happened
The issue involves Citrix NetScaler, a product used by large organisations such as hospitals, banks, and government agencies to manage network traffic and provide secure remote access. Patients rely on systems built with NetScaler to view their medical records online.
Over the weekend, the National Cyber Security Centre (NCSC) warned of critical vulnerabilities in NetScaler. Z-CERT, which specialises in healthcare cybersecurity, advised hospitals to take precautionary measures, including temporarily disabling vulnerable systems. Several hospitals followed this advice. As a result, patients at affected hospitals could not access their records during online consultations, although doctors within the hospitals retained access.
Hospitals reporting issues included Amphia Ziekenhuis in Breda, Elisabeth-TweeSteden Ziekenhuis (ETZ) in Tilburg and Waalwijk, and Frisius MC in Leeuwarden. The disruption extended beyond healthcare, as the interior ministry reported that some civil servants were unable to work remotely after its Citrix applications were disabled.
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A precaution, not a breach
The hospitals emphasised that this was not a cyberattack and that no patient data was compromised. Disabling the systems was a proactive security measure, taken on the advice of security agencies.
The caution was warranted because the flaw was serious and already being exploited. According to the NCSC, Citrix issued security warnings for eight vulnerabilities, including two zero-days that were actively targeted. The most severe ones allow attackers to execute commands remotely without authentication, granting deep system access. The US cybersecurity agency CISA also issued an alert, noting that attackers were exploiting these vulnerabilities worldwide.
Fixed, for now
Citrix has released software updates to address the vulnerabilities, and the NCSC reports that the issues have been resolved. It urges affected organisations to install the patches promptly and continue monitoring for suspicious activity. Frisius MC reported that its systems were fully restored, and other hospitals are bringing services back online.
A recurring weak point
This is not the first time NetScaler has caused issues in the Netherlands. Last year, the public prosecution service (OM) disconnected its systems from the internet for over two months after hackers exploited a vulnerability in the same software, in what the NCSC described as a sophisticated attack. The continued vulnerability of such widely used infrastructure is concerning, especially amid repeated warnings from Dutch intelligence services that cyber threats are increasing. While the immediate inconvenience for patients was limited, the broader concern is the reliance of critical Dutch infrastructure on software frequently targeted by attackers.