According to a recent discovery by Varonis Threat Labs, two new techniques have emerged that pose a significant threat to data security within SharePoint, a widely used platform for file management. These techniques enable users to evade detection and retreat files without triggering alarm bells in audit logs.
Technique 1: Open in App Method
The first technique leverages SharePoint's "open in app" feature, allowing users to access and download files while leaving behind only access events in the file's audit log. This method, which can be executed manually or through automated scripts, enables rapid exfiltration of multiple files without raising suspicion.
Technique 2: SkyDriveSync User-Agent
The second technique exploits the User-Agent for Microsoft SkyDriveSync, disguising file downloads as sync events rather than standard downloads. By mislabeling events, threat actors can bypass detection tools and policies, making their activity harder to track.
Implications for Security
These techniques pose a significant challenge to traditional security tools such as cloud access security brokers and data loss prevention systems. By hiding downloads as less suspicious access and sync events, threat actors can circumvent detection measures and potentially exfiltrate sensitive data unnoticed.
Microsoft's Response
Despite Varonis disclosing these methods to Microsoft, the tech giant has designated them as a "moderate" security concern and has not taken immediate action to address them. As a result, these vulnerabilities remain in SharePoint deployments, leaving organisations vulnerable to exploitation.
Recommendations for Organisations
To alleviate the risk posed by these techniques, organisations are advised to closely monitor access events in their SharePoint and OneDrive audit logs. Varonis recommends leveraging User and Entity Behavior Analytics (UEBA) and AI features to detect and stop suspicious activities, such as mass file access.
What Are the Risks?
While SharePoint and OneDrive are essential tools for facilitating file access in organisations, misconfigured permissions and access controls can inadvertently expose sensitive data to unauthorised users. Threat actors often exploit these misconfigurations to exfiltrate data, posing a significant risk to organisations across various industries.
Detection and Prevention Strategies
To detect and prevent unauthorised data exfiltration, organisations should implement detection rules that consider behavioural patterns, including frequency and volume of sync activity, unusual device usage, and synchronisation of sensitive folders. By analysing these parameters, organisations can identify and mitigate potential threats before they escalate.
