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Fragmented ICMP packets cause FEB and FPC socket disconnection from chassis

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Article ID: JSA10500 SECURITY_ADVISORIES Last Updated: 09 May 2013Version: 6.0
Legacy Advisory Id:
PSN-2011-07-298
Product Affected:
This issue can affect any routing platform listed below, running Junos OS.
Problem:

After receiving a burst of fragmented ICMP packets, the chassis loses connection to the FEB and FPC. The chassisd connection to FRU is terminated, and FEB and FPC reboot, causing a permanent interruption of forwarding. Administrative connection to the FEB or FPCs is impossible via 'vty' or 'cty'. The router must be rebooted to restore administrative connectivity to the FEB or FPCs and resume normal operation.

This issue is specific to interface em0. J Series and SRX Branch models do not have an em0 interface, and are therefore not affected by this issue.
Solution:

Within the internal driver, the number of mbufs in the failed packet were greater than the number of segments that can be mapped into memory. The packet fails to be sent out and failure on the packet causes the driver to prepend the packet into the ifq. The driver keeps retrying to send the packet and fails, the other packets in the queue never get a chance to be sent out.

The number of mbufs utilized is now reduced through defragmentation within the driver code.

All Junos software releases built on or after 2011-07-01 have fixed this specific issue. Releases containing the fix specifically include: 9.3S23, 10.0S17, 10.4R5, 11.1R3, 11.2R1, and all subsequent releases (i.e. all releases built after 11.2R1).

This issue is being tracked as PR 562421. While this PR may not viewable by customers, it can be used as a reference when discussing the issue with JTAC.

KB16765 - "In which releases are vulnerabilities fixed?" describes which release vulnerabilities are fixed as per our End of Engineering and End of Life support policies.

Workaround:

Today's network infrastructure typically will not have fragmented packets destined for the router's control or management plane. In most cases, it is safe to apply packet filters which will prevent fragmented packets from arriving on the router. Usually, fragmented packets received by a router indicate a problem with the network or a DDOS attack against the router. In either case, fragmented packets should be dropped to protect the router's control and management plane.

Below is a sample firewall filter to demonstrate this recommendation:
[edit firewall family inet filter fragment]
user@junos# show
term first-frag {
    from {
        first-fragment;
    }
    then {
        discard;
    }
term next-frag {
    from {
        is-fragment;
    }
    then {
        discard;
    }
Caution: Some routing protocols, such as BGP and OSPF, may rely upon fragmented traffic being received by the RE. As with any control plane firewall filter, perform careful testing in your environment to insure that dropping all fragmented traffic will not have a negative impact. If necessary, add explicit exceptions for fragmented BGP and/or OSPF traffic to the sample firewall filter above.

Note that some platforms -- most notably the EX Series -- do not support the 'first-fragment' filter criterion. In these cases, simply discarding all fragments via 'is-fragment' will be sufficient. Additionally, the EX-8200 does not support either criteria, in which case the only option is to upgrade.

The trigger for this issue is specific to fragmented ICMP packets. While the recommendation of the Juniper Networks SIRT and a security best common practice is to discard all fragments destined to the router's control plane, customers who wish to more specifically define this sample filter may add an additional criterion, 'protocol icmp', to each term. This will cause the filter to only discard fragmented ICMP packets.
Implementation:

How to obtain fixed software:
Security vulnerabilities in Junos are fixed in the next available Maintenance Release of each supported Junos version. In some cases, a Maintenance Release is not planned to be available in an appropriate time-frame. For these cases, Service Releases are made available in order to be more timely. Security Advisory and Security Notices will indicate which Maintenance and Service Releases contain fixes for the issues described. Upon request to JTAC, customers will be provided download instructions for a Service Release. Although Juniper does not provide formal Release Note documentation for a Service Release, a list of "PRs fixed" can be provided on request.
CVSS Score:
6.1 (AV:A/AC:L/Au:N/C:N/I:N/A:C)
Severity Level:
High
Severity Assessment:
Information for how Juniper Networks uses CVSS can be found at KB 16446 "Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories."

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