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Kernel crash after ICMP6 MTU exceeded packet received



Article ID: JSA10457 SECURITY_ADVISORIES Last Updated: 27 Oct 2016Version: 5.0
Legacy Advisory Id:
Product Affected:
This issue affects all hardware platforms running Junos 9.3 or later with the IPv6 address family and IPv6 PATH MTU Discovery enabled.

With IPv6 PATH MTU Discovery enabled (the default), the Junos routing kernel can crash when a malformed ICMPv6 "Packet Too Big" message is received that would trigger a PRC_MSGSIZE (message size forced drop) command to the routine udp6_ctlinput(). This routine is the notification handler used when UDP operates over IPv6.

This issue is not easily reproducible, and a packet triggering this crash should not be seen in a normal network. Exploiting this crash would require a highly specialized crafted packet.

The udp6_ctlinput() function was lacking a NULL check and the kernel crashed as a result of dereferencing a NULL pointer. The fix takes care of initializing this pointer properly prior to fetching the value.

All Junos software releases built on or after 2009-10-09 have fixed this specific issue. Releases containing the fix specifically include: 9.3R4, 9.6R1, 10.0R1 and all subsequent releases (i.e. all releases built after 10.0R1). Note that releases prior to Junos 9.3 are unaffected by this vulnerability.

This issue is being tracked as PR 456161. While this PR is 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.


Apply a firewall filter to the loopback interface to protect against ICMPv6 packet-too-big messages. For example:

        term icmp6-pkt2big {
            from {
                next-header icmpv6;
                icmp-type packet-too-big;
            then {
                count pkt2big;
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.

Modification History:

2010-10-12: Initial publication
2016-10-27: Updated and corrected CVSS score to CVSSv3

CVSS Score:
7.5 (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
Severity Level:
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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