Source: cve@mitre.org
A later variation on the Teardrop IP denial of service attack, a.k.a. Teardrop-2.
CVE-1999-0104 describes a denial-of-service (DoS) vulnerability, a variant of the Teardrop attack, that exploits vulnerabilities in how operating systems handle fragmented IP packets. This attack can lead to system crashes and network outages by sending crafted packets that cause the target system to become unstable due to improper reassembly of fragmented IP packets. The impact is significant, potentially disrupting critical services and causing data loss.
Step 1: Packet Fragmentation: The attacker crafts a series of IP packets, fragmenting them into smaller pieces. These fragments are designed to be overlapping or have incorrect offset values.
Step 2: Fragment Delivery: The attacker sends the crafted IP fragments to the target system.
Step 3: Reassembly Attempt: The target system's IP stack receives the fragmented packets and attempts to reassemble them based on the fragment offset and identification fields.
Step 4: Exploitation: Due to the overlapping or malformed fragments, the reassembly process fails, leading to memory corruption, a buffer overflow, or other memory-related errors within the IP stack.
Step 5: Denial of Service: The memory corruption causes the system to crash, freeze, or become unresponsive, resulting in a denial-of-service condition.
The vulnerability lies in the handling of fragmented IP packets. The Teardrop attack exploits flaws in the reassembly logic of the IP protocol stack within the operating system. Specifically, it sends a series of fragmented IP packets with overlapping or malformed fragment offset fields. When the target system attempts to reassemble these packets, the overlapping or malformed offsets cause the system to allocate excessive memory, leading to a buffer overflow or other memory corruption issues. This can result in a kernel panic, system crash, or denial of service. The root cause is a lack of proper input validation and error handling when processing fragmented packets, allowing attackers to craft packets that trigger unexpected behavior in the reassembly process. The specific function or logic flaw is within the IP fragment reassembly code, where the system fails to correctly handle overlapping or out-of-order fragments, leading to memory corruption.
While no specific APTs are known to actively use this exact variant, the techniques employed are fundamental and could be adapted. The attack vector is more of a historical concern and is not listed on the CISA KEV list.
Network Intrusion Detection Systems (NIDS) can be configured to detect malformed IP fragments, overlapping fragments, or packets with unusual offset values.
Packet capture and analysis using tools like Wireshark can reveal the presence of fragmented packets with suspicious characteristics.
System logs may show errors related to IP packet processing or memory allocation, especially during a denial-of-service event.
Monitor network traffic for an unusual increase in fragmented packets, especially those with overlapping or out-of-order fragment offsets.
Ensure that the operating system is up-to-date with the latest security patches. This includes patches addressing vulnerabilities in the IP stack.
Implement network-based intrusion detection and prevention systems (IDS/IPS) to detect and block malformed IP packets.
Configure firewalls to filter out fragmented packets or to limit the rate of fragmented packets, especially from untrusted sources.
Consider using network segmentation to isolate critical systems from potentially vulnerable network segments.
Regularly audit network traffic for suspicious patterns, including an unusual increase in fragmented packets.
Disable IP fragmentation at the source if possible. This reduces the attack surface.