Data exfiltration in messaging apps through unfurling exploits the feature where apps automatically generate previews for shared links. This process, called unfurling, involves fetching metadata (like titles, descriptions, or images) from the linked resource. Attackers can abuse this mechanism by crafting malicious links that, when shared, cause the app to fetch sensitive data from internal servers or leak tokens, cookies, or other confidential information.
For example, when a user sends a link, the app’s server might access the linked resource to generate a preview. If the server is on an internal network, attackers can include URLs pointing to internal endpoints, tricking the app into exposing sensitive data during the unfurling process. This vulnerability is particularly concerning in enterprise messaging platforms, where such attacks might expose internal APIs, configuration details, or sensitive documents.
Mitigating the risk involves limiting what metadata can be fetched, enforcing strict URL validation, and sandboxing the unfurling process to prevent access to sensitive or internal resources. Users and administrators should also be cautious about sharing unknown or untrusted links in messaging apps.