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2021-04 Security Bulletin: Junos OS and Junos OS Evolved: MX Series with MPC10/MPC11, PTX10003, PTX10008: Line card may crash and restart when traffic is hitting a firewall filter having a term with syslog action configured (CVE-2021-0264)



Article ID: JSA11155 SECURITY_ADVISORIES Last Updated: 14 Apr 2021Version: 2.0
Product Affected:
This issue affects Junos OS 19.3, 19.4, 20.1, 20.2, 20.3, 20.4. Affected platforms: MX Series. This issue affects Junos OS Evolved. Affected platforms: PTX10003, PTX10008.

A vulnerability in the processing of traffic matching a firewall filter containing a syslog action in Juniper Networks Junos OS on MX Series with MPC10/MPC11 cards installed, PTX10003 and PTX10008 Series devices, will cause the line card to crash and restart, creating a Denial of Service (DoS). Continued receipt and processing of packets matching the firewall filter can create a sustained Denial of Service (DoS) condition.

When traffic hits the firewall filter, configured on lo0 or any physical interface on the line card, containing a term with a syslog action (e.g. 'term <name> then syslog'), the affected line card will crash and restart, impacting traffic processing through the ports of the line card.

This issue only affects MX Series routers with MPC10 or MPC11 line cards, and PTX10003 or PTX10008 Series packet transport routers.

No other platforms or models of line cards are affected by this issue.

Note: This issue has also been identified and described in technical service bulletin TSB17931 (login required).

This issue affects:

  • Juniper Networks Junos OS on MX Series:
  • 19.3 versions prior to 19.3R3-S2;
  • 19.4 versions prior to 19.4R3-S2;
  • 20.1 versions prior to 20.1R3;
  • 20.2 versions prior to 20.2R2-S2, 20.2R3;
  • 20.3 versions prior to 20.3R3;
  • 20.4 versions prior to 20.4R2.

Juniper Networks Junos OS Evolved on PTX10003, PTX10008:

  • All versions prior to 20.4R2-EVO.

This issue does not affect Juniper Networks Junos OS versions prior to 19.3R1.

An example of a vulnerable configuration is shown below:

user@router>show configuration firewall family inet filter protect-re | display set
set firewall family inet filter protect-re term reject-everything-else then count discard-counter
set firewall family inet filter protect-re term reject-everything-else then syslog
set firewall family inet filter protect-re term reject-everything-else then discard

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

This issue was seen during production usage.

This issue has been assigned CVE-2021-0264.


The following software releases have been updated to resolve this specific issue:

Junos OS: 19.4R3-S2, 20.1R3, 20.2R2-S2, 20.2R3, 20.3R3, 20.4R2, 21.1R1, and all subsequent releases.
Junos OS Evolved: 20.4R2-EVO, 21.1R1-EVO, and all subsequent releases.

This issue is being tracked as 1559174.

Remove the "syslog" action from the firewall filter configuration.
Software releases or updates are available for download at
Modification History:
2021-04-14: Initial Publication.

CVSS Score:
5.9 (CVSS:3.1/AV:N/AC:H/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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