Support Support Downloads Knowledge Base Juniper Support Portal Community

Knowledge Base

Search our Knowledge Base sites to find answers to your questions.

Ask All Knowledge Base Sites All Knowledge Base Sites JunosE Defect (KA)Knowledge BaseSecurity AdvisoriesTechnical BulletinsTechnotes Sign in to display secure content and recently viewed articles

2021-04 Security Bulletin: Junos OS: PTX Series, QFX10K Series: A PTX/QFX FPC may restart unexpectedly with the "inline-Jflow" feature enabled on a large-scale deployment (CVE-2021-0270)



Article ID: JSA11161 SECURITY_ADVISORIES Last Updated: 14 Apr 2021Version: 4.0
Product Affected:
This issue affects Junos OS 18.1. Affected platforms: PTX Series, QFX10K Series.

On PTX Series and QFX10k Series devices with the "inline-jflow" feature enabled, a use after free weakness in the Packet Forwarding Engine (PFE) microkernel architecture of Juniper Networks Junos OS may allow an attacker to cause a Denial of Service (DoS) condition whereby one or more Flexible PIC Concentrators (FPCs) may restart. As this is a race condition situation this issue become more likely to be hit when network instability occurs, such as but not limited to BGP/IGP reconvergences, and/or further likely to occur when more active "traffic flows" are occurring through the device. When this issue occurs, it will cause one or more FPCs to restart unexpectedly. During FPC restarts core files will be generated. While the core file is generated traffic will be disrupted. Sustained receipt of large traffic flows and reconvergence-like situations may sustain the Denial of Service (DoS) situation.

This issue affects:

Juniper Networks Junos OS:

  • 18.1 version 18.1R2 and later versions prior to 18.1R3-S10 on PTX Series, QFX10K Series.

The inline flow monitoring configuration can be broadly classified into the following categories:

Configurations at the [edit services flow-monitoring version-ipfix template] or [edit services flow-monitoring version9 template] hierarchy level—At this level, you configure the template properties for inline flow monitoring.

Configurations at the [edit forwarding-options sampling instance] hierarchy level—At this level, you configure a sampling instance and associate the template to the sampling instance. At this level, you also configure the flow-server IP address and port number as well as the autonomous system type.

Configurations at the [edit chassis fpc] hierarchy level—At this level, you associate the sampling instance with the FPC on which the media interface is present.

Configurations at the [edit firewall] hierarchy level—At this level you configure a firewall filter for the family of traffic to be sampled. You must attach this filter to the interface on which you want to sample the traffic.

See for further details.

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-2021-0270.


The following software releases have been updated to resolve this specific issue: 16.1R7-S8, 17.2R3-S4, 17.3R3-S8, 17.4R2-S11, 17.4R3-S2, 18.1R3-S10, 18.2R1, and all subsequent releases.

This issue is being tracked as 1498427.


If you are susceptible to this issue and unable to upgrade to software with the fix, you can deploy a workaround by disabling the “inline-flow” feature.

To check for use and to disable the “inline-jflow” service on a device, see for additional details.

Removing “inline-jflow” takes effect immediately and there is no need to restart the FPCs or the router. Once the feature is removed, the router no longer provides traffic data to the flow collector.

Software releases or updates are available for download at
Modification History:
2021-04-14: Initial Publication.
2021-04-14: Added QFX after PTX on FPC.

CVSS Score:
7.5 (CVSS:3.1/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."

Related Links

Comment on this article > Affected Products Browse the Knowledge Base for more articles related to these product categories. Select a category to begin.

Getting Up and Running with Junos

Getting Up and Running with Junos Security Alerts and Vulnerabilities Product Alerts and Software Release Notices Problem Report (PR) Search Tool EOL Notices and Bulletins JTAC User Guide Customer Care User Guide Pathfinder SRX High Availability Configurator SRX VPN Configurator Training Courses and Videos End User Licence Agreement Global Search