Source: cve@mitre.org
Open Projects Network Internet Relay Chat (IRC) daemon u2.10.05.18 does not perform a double-reverse DNS lookup, which allows remote attackers to spoof any valid hostname on the Internet. NOTE: a followup post suggests that this is not an issue in the daemon.
CVE-2001-1488 describes a vulnerability in the Open Projects Network IRC daemon (u2.10.05.18) that allows remote attackers to spoof hostnames due to a failure to perform a double-reverse DNS lookup. This could lead to misidentification of users and potentially allow attackers to bypass access controls or impersonate legitimate users within the IRC network. However, a follow-up post suggests the vulnerability may not exist in the daemon.
Step 1: Attacker Configuration: The attacker configures their system with a desired hostname (e.g., a legitimate user's hostname).
Step 2: Reverse DNS Setup: The attacker ensures that their IP address resolves to the desired hostname through a reverse DNS record (PTR record). This is typically controlled by the attacker's ISP or hosting provider.
Step 3: IRC Connection: The attacker connects to the vulnerable IRC server.
Step 4: Hostname Presentation: The IRC server performs a reverse DNS lookup on the attacker's IP address, which now resolves to the attacker's spoofed hostname.
Step 5: Lack of Double-Check: Because the server does not perform a double-reverse DNS lookup, it accepts the spoofed hostname as valid.
Step 6: Spoofing Success: The attacker's connection is now displayed with the spoofed hostname, potentially allowing them to impersonate other users or bypass access controls.
The vulnerability stems from the IRC daemon's insufficient validation of client hostnames. Specifically, the daemon fails to perform a double-reverse DNS lookup. A double-reverse DNS lookup involves resolving the IP address to a hostname, and then resolving the hostname back to an IP address. If the two IP addresses match, the hostname is considered valid. Without this check, an attacker can provide a hostname that resolves to their IP address, effectively spoofing their identity. The root cause is a lack of proper input validation and a reliance on a single reverse DNS lookup, creating a trust boundary that can be easily circumvented. The vulnerability's impact is limited to the IRC network itself, primarily affecting user identification and potentially access control mechanisms.
Due to the age and nature of the vulnerability, it is unlikely to be directly targeted by modern APTs or malware. This vulnerability is not listed on the CISA KEV catalog.
Review IRC server logs for suspicious hostname entries, particularly those that appear inconsistent with known user behavior or network topology.
Analyze network traffic for unusual DNS queries and responses, specifically those related to reverse DNS lookups.
Implement a network intrusion detection system (IDS) with rules to identify potential hostname spoofing attempts. This could involve monitoring for discrepancies between forward and reverse DNS records.
Monitor IRC server configuration for any custom settings that might disable or weaken hostname verification.
If the IRC daemon is still in use, ensure it is updated to the latest version or a version that addresses this vulnerability (though the follow-up post suggests it may not be present).
Implement a double-reverse DNS lookup check within the IRC server configuration, if available. This is the most direct mitigation.
Configure the IRC server to use a more robust authentication mechanism, such as SSL/TLS, to verify user identities.
Review and harden the IRC server's access control lists (ACLs) to restrict access based on IP address or other verifiable credentials, rather than solely relying on hostnames.
Regularly monitor and audit IRC server logs for suspicious activity.