CVE-2021-31371Network attack vector

Information exposure via internal-network packet egress

Published Oct 19, 2021 · Updated Sep 17, 2024

Information exposure in Juniper Networks Junos OS on affected QFX5000 switches allows remote attackers to read internal device data. The forwarding path permits packets sourced from the RE-PFE internal 128.0.0.0/2 network to leave egress interfaces instead of containing them within the switch. No authentication or user interaction is required; exposed traffic can reveal heartbeats, kernel versions, and other configuration information.

CVSS severity5.3
Medium
EPSS probability0.84%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information exposure in Juniper Networks Junos OS on affected QFX5000 switches allows remote attackers to read internal device data. The forwarding path permits packets sourced from the RE-PFE internal 128.0.0.0/2 network to leave egress interfaces instead of containing them within the switch. No authentication or user interaction is required; exposed traffic can reveal heartbeats, kernel versions, and other configuration information.

The record

CVE
CVE-2021-31371
Published
Oct 19, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-200, T1040
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=18.1 <18.1R3-S13
  2. Affected versionversion=18.3 <18.3R3-S5
  3. Affected versionversion=19.1 <19.1R3-S6
  4. Affected versionversion=19.2 <19.2R1-S7, 19.2R3-S3
  5. Affected versionversion=19.3 <19.3R2-S6, 19.3R3-S3
  6. Affected versionversion=19.4 <19.4R1-S4, 19.4R3-S5
  7. Affected versionversion=20.1 <20.1R2-S2, 20.1R3-S1
  8. Affected versionversion=20.2 <20.2R3-S2
  9. Affected versionversion=20.3 <20.3R3-S1
  10. Affected versionversion=20.4 <20.4R2-S1, 20.4R3
  11. Affected versionversion=21.1 <21.1R1-S1, 21.1R2
  12. Affected versionversion=21.2 <21.2R1
  13. Affected versionversion=unspecified <17.3R3-S12

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=18.1 <18.1R3-S13; version=18.3 <18.3R3-S5; version=19.1 <19.1R3-S6; version=19.2 <19.2R1-S7, 19.2R3-S3; version=19.3 <19.3R2-S6, 19.3R3-S3; version=19.4 <19.4R1-S4, 19.4R3-S5; version=20.1 <20.1R2-S2, 20.1R3-S1; version=20.2 <20.2R3-S2; version=20.3 <20.3R3-S1; version=20.4 <20.4R2-S1, 20.4R3; version=21.1 <21.1R1-S1, 21.1R2; version=21.2 <21.2R1; version=unspecified <17.3R3-S12

Published CVSS scores

5.3Juniper Networks, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-200Exposure of Sensitive Information to an Unauthorized Actor
T1040Network Sniffing

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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