Fireshare allows an attacker who can authenticate to the system to craft a multipart request to the /api/uploadChunked endpoint that contains a "checkSum" field. The value of this field is concatenated directly into a filesystem path without any sanitization or containment checks, enabling a path traversal attack that writes an arbitrary file to any location writable by the Fireshare process. This breach of file system integrity can lead to placement of malicious executables, configuration manipulation, or other follow‑on attacks depending on how the application and host system are configured.

The vulnerability affects ShaneIsrael's Fireshare product, specifically version 1.5.1. The release notes for version 1.5.2 contain a fix that removes the unsanitized path construction. Users running version 1.5.1 or earlier are at risk.

The CVSS score of 7.1 indicates a high impact severity, and while no EPSS score is available, the lack of exploitation evidence suggests moderate to high risk for compromised accounts. The vulnerability is not listed in CISA’s KEV catalog, implying it has not yet become a widely known exploit. Attackers require authenticated access to the Fireshare service to send the malicious payload, but once authenticated, they can deploy arbitrary files to writable locations such as /tmp in a container environment, potentially enabling file execution or persistent compromise.