filebrowser Sets Insecure File Permissions

Summary

The file access permissions for files uploaded to or created from File Browser are never explicitly set by the application. The same is true for the database used by File Browser. On standard servers where the umask configuration has not been hardened before, this makes all the stated files readable by any operating system account.

Impact

The default permissions for new files on a standard Linux system are 0644, making them world-readable. That means that at least the following parties have full read access to all files managed by the Filebrowser from all scopes, as well as its database (including the password hashes stored in there):

• All OS accounts on the server
• All other applications running on the same server
• Any Filebrowser user with Command Execution privileges having access to a command that allows reading a file's content

Vulnerability Description

On a Linux system, the file access permissions of new files are designated by the system wide umask setting, unless they are configured manually. Most distributions set this value to 022 by default which gives every account on the system read permissions on the file.

$ umask
022
$ touch foo
$ ls -l foo
-rw-r--r-- 1 sba sba 0 31. Mär 15:08 foo

Proof of Concept

Upload or create a file in the Filebrowser GUI and list the directory contents from a shell:

$ ls -l /srv/filebrowser/testdir
total 12
-rw-r--r-- 1 sba sba 7703 Mar 25 16:07 dummy1.pdf
-rw-r--r-- 1 sba sba    3 Mar 25 15:46 testfile.txt

The same can be validated for Docker based deployments within the container:

$ docker exec -it e0f075082a2c ls /srv/testdir -l
total 12
-rw-r--r--    1 1000     1000          7703 Mar 25 15:07 dummy1.pdf
-rw-r--r--    1 1000     1000             3 Mar 25 14:46 testfile.txt

Furthermore, the database used by the Filebrowser application is readable by any account:

$ ls -l /srv/filebrowser/filebrowser.db 
-rw-rw-r-- 1 sba sba 65536 Mar 25 09:58 /srv/filebrowser/filebrowser.db

Recommended Countermeasures

Since the system's umask configuration cannot be controlled by the Filebrowser, the application needs to set the permissions of all new files manually upon creation. No permissions should be given to the other category.

Implementing this won't fix the permissions for active instances after an update, so site administrators will need to fix the permissions manually:

$ chmod o-rwx -R /srv/filebrowser/datadir

Timeline

• 2025-03-25 Identified the vulnerability in version 2.32.0
• 2025-04-11 Contacted the project
• 2025-04-18 Vulnerability disclosed to the project
• 2025-06-25 Uploaded advisories to the project's GitHub repository
• 2025-06-26 CVE ID assigned by GitHub
• 2025-06-26 Fix released with version 2.33.7

References

• CWE-276: Incorrect Default Permissions
• What is Umask and How To Setup Default umask Under Linux?
• Original Advisory

Credits

• Mathias Tausig (SBA Research)