Source: cve@mitre.org
Cisco routers 9.17 and earlier allow remote attackers to bypass security restrictions via certain IP source routed packets that should normally be denied using the "no ip source-route" command.
Cisco routers running versions 9.17 and earlier are vulnerable to a critical security flaw allowing remote attackers to bypass the 'no ip source-route' command. This vulnerability permits attackers to inject malicious traffic, potentially leading to network compromise and data exfiltration by exploiting source routing.
Step 1: Crafting the Malicious Packet: The attacker crafts a malicious IP packet. This packet includes the IP source route option in the IP header, specifying a path through the network that the attacker desires. This path is designed to bypass the 'no ip source-route' command.
Step 2: Packet Delivery: The attacker sends the crafted packet to the vulnerable Cisco router.
Step 3: Bypassing the Restriction: The router, due to the vulnerability, fails to correctly enforce the 'no ip source-route' command. The packet is not dropped or rejected as it should be.
Step 4: Packet Processing: The router processes the packet according to the source route specified in the IP header. This allows the packet to traverse the network along the attacker-defined path.
Step 5: Network Access: The attacker can now send traffic to internal network resources that would normally be inaccessible, potentially leading to further exploitation and network compromise.
The vulnerability stems from an improper handling of IP source-routed packets within the Cisco router's network stack. The 'no ip source-route' command is intended to disable the processing of source-routed packets, preventing attackers from specifying the path a packet should take through the network. However, a flaw in the packet processing logic allows specifically crafted source-routed packets to bypass this restriction. The root cause is likely a failure to correctly validate or filter these packets before they are processed by the routing engine, allowing attackers to manipulate the packet's destination and potentially gain unauthorized access to internal network resources. This could be due to a logic error in the packet filtering code or an issue in how the router handles the source route option within the IP header.
This vulnerability, while old, highlights a fundamental network security weakness. While no specific APTs are directly linked to this CVE, the technique of source route manipulation is a common tactic. The potential impact of this vulnerability is significant, as it could allow attackers to bypass network segmentation and access sensitive internal resources. This vulnerability is not listed on the CISA KEV.
Monitor network traffic for IP packets with the source route option enabled (IP header option 0x83).
Analyze router logs for packets that should have been dropped due to the 'no ip source-route' configuration but were processed.
Implement network intrusion detection systems (IDS) with rules specifically designed to detect and alert on source-routed packets.
Examine network traffic for unusual patterns or destinations that might indicate unauthorized access.
Upgrade Cisco routers to a version that addresses the vulnerability (9.18 or later).
Verify that the 'no ip source-route' command is enabled on all relevant interfaces.
Implement strong network segmentation to limit the impact of a potential compromise.
Regularly audit network configurations to ensure security best practices are followed.
Consider using network access control lists (ACLs) to further restrict traffic based on source and destination IP addresses.