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Security Advisory - Certain packet sequences can cause router interfaces to permanently block packet processing (CERT Advisory CA-2003-15)



Article ID: JSA10314 SECURITY_ADVISORIES Last Updated: 09 May 2013Version: 3.0
Legacy Advisory Id:
Product Affected:
It was recently discovered that a handcrafted sequence of IPv4 packets could be used to launch a denial-of-service (DoS) attack against certain routers and other packet-forwarding devices in the Internet. This vulnerability takes advantage of a software bug that improperly manages input packet buffers and is described in more detail at the URL below.
This vulnerability affects products of a single vendor other than Juniper Networks. The packet buffer management scheme used in Juniper Networks products is not susceptible to this vulnerability.
No solution is required to protect Juniper Networks routers.

The JUNOS Internet Software includes a firewall filter capability that can be deployed to protect a network from exposure to this vulnerability. Configure the following firewall filter on an M-series or T-series router, and apply it as an input filter on the router's edge-facing interfaces to block all incoming packets that can be used to take advantage of this vulnerability.
user@router# show firewall filter protect
term block-bad-protos {
      from {
            protocol [53 55 77 103];
      then discard;
term permit-others {
      then accept;

# set interface  unit  family inet filter input protect

If you already have a firewall filter assigned to the edge-facing interfaces, simply insert the first term from the above example at the beginning of the existing firewall filter.

On Juniper Networks E-series routers running JUNOSe software, configure the following filtering policy and apply it to edge-facing interfaces. In this filtering policy you use a classifier list to identify the affected protocols, define a policy referencing the classifier list, and finally apply the policy to the appropriate interfaces:
1400# config t
1400(config)#classifier-list protect-network 53 any any
1400(config)#classifier-list protect-network 55 any any
1400(config)#classifier-list protect-network 77 any any
1400(config)#classifier-list protect-network 103any any
1400(config)#policy-list protect-network
1400(config-policy-list)#filter classifier-group protect-network
1400(config)#interface gig 4/0
1400(config-if)#ip policy input protect-network statistics enabled
Note that these filters block all packets for protocols 53 (SWIPE), 55 (IP Mobility), 77 (SUN ND), and 103 (PIM). While the first three protocols are rarely found in the Internet, PIM (Protocol Independent Multicast) is commonly used in multicast-enabled networks. If your network uses PIM, you must create a more complex filter to selectively block unwanted PIM packets.
Severity Level:
Severity Assessment:
Juniper Networks products use a different, proprietary packet buffer management scheme and are not susceptible to this vulnerability.

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