File Browser: Command Injection via Authentication Hook Shell Substitution (Pre-Authentication RCE)

The Hook Authentication feature in File Browser allows administrators to delegate login verification to an external shell command. User-supplied credentials (username and password) are interpolated into this command string using os.Expand without sanitization. An unauthenticated remote attacker can inject shell metacharacters in the username or password field at the login screen, causing the server to execute arbitrary OS commands before any authentication takes place. This is a critical pre-authentication RCE.

• File: auth/hook.go
• Function: HookAuth.RunCommand

Vector String: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Base Score: 9.3 (Critical)

Note: PR:None is the critical differentiator from vulnerabilities 01 and 02. Because the injection point is the unauthenticated login endpoint, no account or session is required. A single HTTP request to the login API is sufficient to achieve RCE.

HookAuth.RunCommand builds the authentication command and substitutes credential values using os.Expand:

 1// auth/hook.go
 2envMapping := func(key string) string {
 3    switch key {
 4    case "USERNAME":
 5        return a.Cred.Username  // directly from the HTTP login request body
 6    case "PASSWORD":
 7        return a.Cred.Password  // directly from the HTTP login request body
 8    default:
 9        return os.Getenv(key)
10    }
11}
12 
13for i, arg := range command {
14    if i == 0 { continue }
15    command[i] = os.Expand(arg, envMapping) // no escaping applied
16}

os.Expand performs plain text substitution. There is no escaping, quoting, or validation of the credential values before they are embedded into the command string.

If an admin has configured the hook authentication command as:

 1sh -c "test $USERNAME = 'admin'"

...and an attacker submits the username ; id # at the login screen, the expanded command becomes:

 1sh -c "test ; id # = 'admin'"

The ; terminates the test expression and the shell executes id. The # comments out the remainder, preventing a syntax error. The attacker's command runs with the privileges of the File Browser process — without needing a valid account or password.

1. Admin enables Hook Authentication and sets the command to:
   bash복사

    1sh -c "test $USERNAME = 'admin'"

2. An unauthenticated attacker sends a login request (e.g., via curl or the web UI) with:
   • Username: ; id #
   • Password: (any value)
3. The server executes:
   text복사

    1sh -c "test ; id # = 'admin'"

4. The id command runs on the server, confirming pre-authentication RCE.

No account is needed. The attacker does not need to know any valid credentials. A single request is sufficient.

An unauthenticated remote attacker can execute arbitrary OS commands on the server under the privilege level of the File Browser process. This is the most severe class of vulnerability in this codebase:

• No authentication required — exposed to the entire internet if the service is public-facing.
• Single request — no setup, no enumeration, no prior foothold.
• Full server compromise: data exfiltration, persistent backdoor installation, lateral movement to internal networks.

Any internet-facing File Browser instance with Hook Authentication enabled is fully compromised by a single malformed login attempt.

Pass credentials exclusively as environment variables, not as shell string substitutions. This feature is undocumented, so removing it should not cause issues.