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CVE-2026-54337 – Unauthenticated Arbitrary File Write/Overwrite – Fireshare < 1.6.14

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Summary

CVE-2026-54337 is a critical argument injection vulnerability (CWE-88) in Fireshare, a self-hosted media and link sharing platform, affecting its public video upload function. The flaw allows unauthenticated attackers to inject arguments into a backend command invocation, resulting in arbitrary file write or overwrite on the underlying system. It carries a CVSS v3.1 score of 9.8 (Critical).

Technical details

  • Root cause: the upload handler sanitizes filenames with secure_filename(), which strips many special characters but does not remove spaces, and the accompanying folder parameter is only checked for forward slashes and .. sequences rather than being fully sanitized.
  • The uploaded file path is passed to an internal video-scan routine that builds a command line (e.g. fireshare scan-video --path=<save_path>); when this command string is later tokenized with a simple split operation, attacker-controlled spaces in the filename/folder values become additional, independently-interpreted arguments.
  • Attack vector: the unauthenticated /api/upload/public endpoint accepts multipart form data (file and folder fields); a crafted filename such as db.sqlite -select_streams v.mp4 combined with a crafted folder value such as testfolder -o data causes the underlying media-probing command to write/overwrite a file at an attacker-chosen path.
  • Impact: no authentication or user interaction is required (network attack vector, low complexity). An attacker can create or overwrite files reachable by the service account (typically limited to the app’s /data, /processed, /images, and /videos directories). Overwriting the application’s SQLite database file renders the service unusable, and arbitrary file write can also be leveraged for further compromise depending on file targets.

Affected software

  • Fireshare (ShaneIsrael/fireshare) — all versions prior to 1.6.14

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade Fireshare to version 1.6.14 or later, which fixes the argument injection issue.
  • If immediate patching is not possible: restrict or disable public/unauthenticated upload functionality, place the application behind authentication or an access-controlled reverse proxy, and monitor/restrict outbound file-system writes from the application’s service account until the upgrade can be applied.

References

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