File Browser vulnerable to insecure password handling

Summary

All user accounts authenticate towards a File Browser instance with a password. A missing password policy and brute-force protection makes it impossible for administrators to properly secure the authentication process.

Impact

Attackers can mount a brute-force attack against the passwords of all accounts of an instance. Since the application is lacking the ability to prevent users from choosing a weak password, the attack is likely to succeed.

Vulnerability Description

The application implement a classical authentication scheme using a username and password combination. While employed by many systems, this scheme is quite error-prone and a common cause for vulnerabilities. File Browser's implementation has multiple weak points:

1. Since the application is missing the capability for administrators to define a password policy, users are at liberty to set trivial and well-known passwords such as secret or even ones with only single digit like 1.
2. New instances are set up with a default password of admin for the initial administrative account. This password is well known and easily guessable. While the documentation advises to change this password, the application does not technically enforce it.
3. The application does not implement any brute-force protection for the authentication endpoint. Attackers can make as many guesses for a password as the network bandwidth allows.

The combination of these problems makes it likely, that an attacker will succeed in compromising at least one account in a File Browser instance, possibly even one with administrative privileges. The likelihood of such an attack increases substantially for internet-facing instances.

Proof of Concept

The insecure default credentials are documented on the application's website:

image

The following HTTP communication shows, that a trivial password of 1 can be configured by a user:

PUT /api/users/2 HTTP/1.1
Host: filebrowser.local:8080
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:128.0) Gecko/20100101 Firefox/128.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Referer: http://filebrowser.local:8080/settings/profile
X-Auth: eyJ[...]
Content-Type: text/plain;charset=UTF-8
Content-Length: 319
Origin: http://filebrowser.local:8080
Connection: keep-alive
Cookie: auth=eyJ[...]
X-PwnFox-Color: cyan
Priority: u=0

{"what":"user","which":["password"],"data":{"id":2,"locale":"en","viewMode":"mosaic","singleClick":false,"perm":{"admin":false,"execute":true,"create":true,"rename":true,"modify":true,"delete":true,"share":true,"download":true},"commands":[],"lockPassword":false,"hideDotfiles":false,"dateFormat":false,"password":"1"}}

HTTP/1.1 200 OK
Cache-Control: no-cache, no-store, must-revalidate
Content-Security-Policy: default-src 'self'; style-src 'unsafe-inline';
Content-Type: text/plain; charset=utf-8
X-Content-Type-Options: nosniff
Date: Thu, 27 Mar 2025 08:31:34 GMT
Content-Length: 7

200 OK

The missing brute-force protection can easily be tested by repeatedly sending the following request to the application with a tool such as Burp or hydra.

POST /api/login HTTP/1.1
Host: filebrowser.local:8080
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:128.0) Gecko/20100101 Firefox/128.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Content-Type: application/json
Content-Length: 52
Origin: http://filebrowser.local:8080

{"username":"admin","password":"myPasswordGuess","recaptcha":""}

HTTP/1.1 403 Forbidden
Cache-Control: no-cache, no-store, must-revalidate
Content-Security-Policy: default-src 'self'; style-src 'unsafe-inline';
Content-Type: text/plain; charset=utf-8
X-Content-Type-Options: nosniff
Date: Thu, 27 Mar 2025 08:39:48 GMT
Content-Length: 14

403 Forbidden

After sending 3000 bad passwords to the application within a few seconds, a successful authentication is still possible for the account:

POST /api/login HTTP/1.1
Host: filebrowser.local:8080
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:128.0) Gecko/20100101 Firefox/128.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Content-Type: application/json
Content-Length: 54
Origin: http://filebrowser.local:8080
Connection: keep-alive

{"username":"admin","password":"myCorrectPassword","recaptcha":""}

HTTP/1.1 200 OK
Cache-Control: no-cache, no-store, must-revalidate
Content-Security-Policy: default-src 'self'; style-src 'unsafe-inline';
Content-Type: text/plain
Date: Thu, 27 Mar 2025 08:39:58 GMT
Content-Length: 508

eyJ[...]

Recommended Countermeasures

The application should add an option to define a password policy in its administrative interface which allows to set a minimum length for passwords. The default settings should be in line with the NIST publication SP 800-63B. This means, that now passwords of fewer than 8 characters should ever be allowed by the application. Whenever a user sets a new password, the application should verify whether that password is part of a "known passwords" list.

The application should either create a secure and random password for the admin account upon initialization or enforce an immediate password change when that user logs in for the first time using the default password.

A brute-force protection needs to be implemented, which limits the allowed amount of authentication attempts per user within a certain timeframe. This implementation should employ device tokens to prevent targeted lockout attacks.

In addition, it would be advisable to allow the integration of the application into and existing Identity Provider using protocols like LDAP or OIDC.

Timeline

• 2025-03-27 Identified the vulnerability in version 2.32.0
• 2025-04-11 Contacted the project
• 2025-04-29 Vulnerability disclosed to the project
• 2025-06-25 Uploaded advisories to the project's GitHub repository
• 2025-06-26 CVE ID assigned by GitHub
• 2025-06-29 Fix released in version 2.34.1. 12 minimum characters as default has been chosen since the implementation does not include protection against brute force attacks.

References

• OWASP Authentication Cheat Sheet
• NIST Special Publication 800-63B. Digital Identity Guidelines. Passwords
• Pwned Passwords
• Common Credentials
• CWE-307: Improper Restriction of Excessive Authentication Attempts
• CWE-521: Weak Password Requirements
• CWE-1392: Use of Default Credentials
• Original Advisory

Credits

• Mathias Tausig (SBA Research)