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2021-10 Security Bulletin: Junos OS: QFX5000 Series: Traffic from the network internal to the device (128.0.0.0) may be forwarded to egress interfaces (CVE-2021-31371)

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Article ID: JSA11236 SECURITY_ADVISORIES Last Updated: 25 Oct 2021Version: 2.0
Product Affected:
This issue affects Junos OS all versions prior to 17.3R3-S12, 18.1, 18.3, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, 20.3, 20.4, 21.1, 21.2. Affected platforms: QFX5000 Series.
Problem:

Juniper Networks Junos OS uses the 128.0.0.0/2 subnet for internal communications between the RE and PFEs. It was discovered that packets utilizing these IP addresses may egress an QFX5000 Series switch, leaking configuration information such as heartbeats, kernel versions, etc. out to the Internet, leading to an information exposure vulnerability.

This issue affects Juniper Networks Junos OS on QFX5110, QFX5120, QFX5200, QFX5210 Series, and QFX5100 with QFX 5e Series image installed:

  • All versions prior to 17.3R3-S12;
  • 18.1 versions prior to 18.1R3-S13;
  • 18.3 versions prior to 18.3R3-S5;
  • 19.1 versions prior to 19.1R3-S6;
  • 19.2 versions prior to 19.2R1-S7, 19.2R3-S3;
  • 19.3 versions prior to 19.3R2-S6, 19.3R3-S3;
  • 19.4 versions prior to 19.4R1-S4, 19.4R3-S5;
  • 20.1 versions prior to 20.1R2-S2, 20.1R3-S1;
  • 20.2 versions prior to 20.2R3-S2;
  • 20.3 versions prior to 20.3R3-S1;
  • 20.4 versions prior to 20.4R2-S1, 20.4R3;
  • 21.1 versions prior to 21.1R1-S1, 21.1R2;

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-2021-31371.

Solution:

The following software releases have been updated to resolve this specific issue: 17.3R3-S12, 18.1R3-S13, 18.3R3-S5, 19.1R3-S6, 19.2R1-S7, 19.2R3-S3, 19.3R2-S6, 19.3R3-S3, 19.4R1-S4, 19.4R3-S5, 20.1R2-S2, 20.1R3-S1, 20.2R3-S2, 20.3R3-S1, 20.4R2-S1, 20.4R3, 21.1R1-S1, 21.1R2, 21.2R1, and all subsequent releases.

This issue is being tracked as 1561722.

Workaround:

Configure a firewall filter to discard packets sourced from the internal network.

Disabling the net.transit_re sysctl flag will also cause management traffic forwarded to the PFE ports to be dropped:

% sysctl -w net.transit_re=0

Note that sysctl flags do not survive a reboot.

Implementation:
Software releases or updates are available for download at https://support.juniper.net/support/downloads/
Modification History:
2021-10-25: Affected platforms updated.
2021-10-13: Initial Publication.
CVSS Score:
5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N)
Severity Level:
Medium
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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