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

published 2021-10-19 5y ago modified 2026-06-17 4mo ago also EUVD-2021-18281

cvss: 5.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.8%; EPSS 0.8% chance of exploitation in 30 days, percentile 58%
public exploits: 0; none known

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;

Patch / fix

fixed in 1

Juniper Networks Junos OS 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

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Exploit prediction

0.84% chance of exploitation in the next 30 days, higher than 58% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by	version	score	vector
CNA	3.1	5.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
NVD	2.0	5.0	AV:N/AC:L/Au:N/C:P/I:N/A:N

Affected products

Juniper Networks Junos OS

Classification

Weakness

CWE-200 Exposure of Sensitive Information to an Unauthorized Actor

References

kb.juniper.net /JSA11236
mitigation, vendor-advisory

Sources

CVE List CVE-2021-31371
NVD CVE-2021-31371

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