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2012-07 Security Bulletin: Junos: When 'log' action is enabled, a firewall filter deployed on lo0 cannot filter high rate of packets sent to the RE

  [JSA10523] Show Article Properties

Legacy Advisory Id:
Product Affected:
This issue can affect all Junos routers configured with 'log' or 'syslog' actions within an lo0 loopback firewall filter.

When enabling 'log' (or 'syslog') and 'discard' actions within a firewall filter term deployed on the lo0 loopback interface to prevent packets from reaching the Routing Engine (RE), if the receive rate is very high, some of the packets will bypass the firewall filter and be received by the RE. An example affected configuration is shown below:
term allow-telnet {
   from {
      protocol tcp;
     destination-port telnet;
    then accept;
    then {
     count deny-others;
Both log/discard and syslog/discard combinations are affected. Note that the rate of packets received by the RE is very low, but depending on the packet content and router configuration, these packets can have a negative impact on routing protocols maintained by the RE.

This issue is specific to R-chip, I-chip and SR-chip PFEs.

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

No other Juniper Networks products or platforms are affected by this issue.

All Junos OS software releases built on or after 2012-05-24 have fixed this specific issue. Releases containing the fix specifically include: 10.0S24, 10.4R10, 11.2R7, 11.4R1, and all subsequent releases (i.e. all releases built after 11.4R1).

This issue is being tracked as PR 676689 and is visible on the Customer Support website.

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.


Disable logging and/or syslog in the firewall filter expression.

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.
Related Links:
CVSS Score:
7.1 (AV:N/AC:M/Au:N/C:N/I:N/A:C)
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."