Source: cve@mitre.org
Denial of service in Ascend and 3com routers, which can be rebooted by sending a zero length TCP option.
Critical network infrastructure is vulnerable to a denial-of-service (DoS) attack. Attackers can remotely crash vulnerable Ascend and 3Com routers by sending a specially crafted TCP packet, leading to service disruption and potential network outages.
Step 1: Target Identification: The attacker identifies Ascend or 3Com routers within the target network.
Step 2: Packet Crafting: The attacker crafts a TCP packet with a zero-length TCP option. This involves setting the TCP option length field to zero.
Step 3: Packet Delivery: The attacker sends the crafted TCP packet to the target router, typically on a port that the router is listening on (e.g., a management port or a port used for network services).
Step 4: Vulnerability Trigger: The router's network stack receives the malformed TCP packet and attempts to process the zero-length option.
Step 5: Denial of Service: Due to the vulnerability, the router crashes, reboots, or becomes unresponsive, resulting in a denial of service.
The vulnerability lies in the handling of TCP options within the router's network stack. Specifically, the routers fail to properly validate the length of a TCP option when a zero-length option is received. This leads to a memory access violation or a NULL pointer dereference when the router attempts to process the malformed option. The root cause is likely a lack of bounds checking or improper handling of the option length field, causing the router to read or write to invalid memory locations. This can trigger a crash or reboot of the device, effectively causing a DoS.
While no specific APT groups are directly linked to this CVE, the ease of exploitation makes it a potential tool for various threat actors, including those seeking to disrupt network operations. This vulnerability is not listed in CISA KEV as of this analysis.
Network Intrusion Detection Systems (NIDS) can be configured to detect packets with zero-length TCP options.
Security Information and Event Management (SIEM) systems can be configured to alert on network traffic patterns indicative of DoS attacks, including a sudden increase in traffic to management ports or a drop in network availability.
Packet capture (PCAP) analysis can be used to identify malicious TCP packets with zero-length options.
Router logs can be reviewed for unexpected reboots or error messages related to TCP processing.
Apply the latest firmware updates from the vendor to patch the vulnerability. This is the most effective mitigation.
Implement network segmentation to isolate critical infrastructure from untrusted networks.
Configure access control lists (ACLs) to restrict access to router management interfaces.
Monitor network traffic for suspicious activity, including packets with zero-length TCP options.
Consider deploying a Web Application Firewall (WAF) or Intrusion Prevention System (IPS) to filter malicious traffic.