Source: cve@mitre.org
The POP3 server in FTGate returns an -ERR code after receiving an invalid USER request, which makes it easier for remote attackers to determine valid usernames and conduct brute force password guessing.
FTGate's POP3 server is vulnerable to a brute-force attack due to its failure to distinguish between invalid usernames and other errors. This allows attackers to efficiently enumerate valid usernames, significantly increasing the likelihood of a successful password-guessing campaign and potential system compromise.
Step 1: Initial Connection: The attacker establishes a TCP connection to the FTGate POP3 server on port 110 (or the configured port).
Step 2: USER Command Iteration: The attacker sends a series of USER <username> commands, substituting different usernames in each attempt.
Step 3: Error Response Analysis: The attacker analyzes the server's response to each USER command. A consistent -ERR response indicates an invalid username (or potentially another error).
Step 4: Username Enumeration: The attacker continues iterating through usernames until a different response is received, indicating a valid username.
Step 5: Password Guessing: Once a valid username is identified, the attacker proceeds to guess the password using the PASS <password> command.
Step 6: Account Compromise: If the correct password is provided, the attacker gains access to the user's email account.
The vulnerability stems from the POP3 server's inadequate error handling. Specifically, the server returns the same generic -ERR response regardless of whether the USER command receives an invalid username or encounters another internal error. This lack of differentiation allows attackers to quickly iterate through potential usernames, as a successful username will eventually elicit a different response (e.g., a prompt for the password). The root cause is a flawed implementation of the authentication protocol, failing to provide distinct error codes for different failure scenarios. This design flaw facilitates a straightforward brute-force attack against the username space.
This vulnerability, while old, could be leveraged by any attacker seeking to gain unauthorized access to email accounts. There are no specific APTs or malware families directly linked to this CVE. However, the ease of exploitation makes it a potential target for opportunistic attackers. CISA KEV status: Not Listed.
Network Intrusion Detection Systems (NIDS) can detect repeated USER command attempts followed by -ERR responses, especially if originating from a single IP address.
Security Information and Event Management (SIEM) systems can analyze POP3 server logs for suspicious activity, such as a high rate of failed login attempts.
Forensic analysis of server logs can reveal the sequence of USER and PASS commands used in a brute-force attack.
Unusual network traffic patterns, such as a high volume of POP3 traffic from a single source, can be indicative of an attack.
Upgrade to a patched version of FTGate or a different POP3 server software that addresses the vulnerability. If no patch is available, consider migrating to a more secure email solution.
Implement account lockout policies to prevent brute-force attacks. After a certain number of failed login attempts, the account should be locked for a period of time.
Enforce strong password policies, requiring users to use complex passwords that are difficult to guess.
Monitor server logs for suspicious activity and implement intrusion detection systems to alert on potential attacks.
Consider implementing multi-factor authentication (MFA) to add an extra layer of security to user accounts.
Restrict access to the POP3 server to only trusted IP addresses or networks.