Junos OS: QFX5000 Series: Traffic from the network internal to the device (128.0.0.0) may be forwarded to egress interfaces.

Description

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;

Scores

EPSS (exploitation in 30 days)

0.84% · top 42% of all CVEs (7 Nov 2026)

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.3.

Weakness

• CWE-200 Information Exposure (opens in a new tab)All about CWE-200 and its CVEs

Affected products

• Juniper Networks · Junos OS

  • affected unspecified – < 17.3R3-S12
  • affected 18.1 – < 18.1R3-S13
  • affected 18.3 – < 18.3R3-S5
  • affected 19.1 – < 19.1R3-S6
  • affected 19.2 – < 19.2R1-S7, 19.2R3-S3
  • affected 19.3 – < 19.3R2-S6, 19.3R3-S3
  • affected 19.4 – < 19.4R1-S4, 19.4R3-S5
  • affected 20.1 – < 20.1R2-S2, 20.1R3-S1
  • affected 20.2 – < 20.2R3-S2
  • affected 20.3 – < 20.3R3-S1
  • affected 20.4 – < 20.4R2-S1, 20.4R3
  • affected 21.1 – < 21.1R1-S1, 21.1R2
  • affected 21.2 – < 21.2R1

What to do

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.

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.

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

References (1)

• https://kb.juniper.net/JSA11236 (opens in a new tab)x_refsource_CONFIRMx_transferred

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2021-31371](https://trackcve.app/badge/CVE-2021-31371.svg)](https://trackcve.app/cve/CVE-2021-31371)

Record last updated 17 Sept 2024, 03:48 UTC.