JunosOperating system · Juniper

CVE-2021-31374

HIGH · 7.5 CVSS v3.1 Published 2021-10-19

Mitigation only

No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.

See remediation →

84/100

Remediation priority · High

Remotely reachable No privileges Zero-click

Official description

NVD · unedited

On Juniper Networks Junos OS and Junos OS Evolved devices processing a specially crafted BGP UPDATE or KEEPALIVE message can lead to a routing process daemon (RPD) crash and restart, causing a Denial of Service (DoS). Continued receipt and processing of this message will create a sustained Denial of Service (DoS) condition. This issue affects both IBGP and EBGP deployments over IPv4 or IPv6. This issue affects: Juniper Networks Junos OS: 17.3 versions prior to 17.3R3-S11; 17.4 versions prior to 17.4R2-S13, 17.4R3-S4; 18.1 versions prior to 18.1R3-S12; 18.2 versions prior to 18.2R2-S8, 18.2R3-S7; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R1-S8, 18.4R2-S7, 18.4R3-S7; 19.1 versions prior to 19.1R1-S6, 19.1R2-S2, 19.1R3-S4; 19.2 versions prior to 19.2R1-S6, 19.2R3-S1; 19.3 versions prior to 19.3R2-S5, 19.3R3-S1; 19.4 versions prior to 19.4R1-S4, 19.4R1-S4, 19.4R2-S3, 19.4R3-S1; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R2; 20.3 versions prior to 20.3R1-S1, 20.3R2. Juniper Networks Junos OS Evolved: 20.3 versions prior to 20.3R2-EVO.

Technical summary

dbcve analysis · high confidence

A specially crafted BGP UPDATE or KEEPALIVE message triggers a vulnerability in the routing process daemon (RPD) on Juniper Networks Junos OS and Junos OS Evolved devices, causing the daemon to crash and restart. Continued receipt of these malicious messages results in a sustained Denial of Service condition, affecting both IBGP and EBGP deployments over IPv4 and IPv6.

MitigationApply the vendor-supplied patches or upgrade to a fixed Junos OS version as listed in the Juniper Networks advisory. Consider implementing BGP traffic filtering or rate limiting as a temporary workaround while planning the upgrade.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions

NVD · CPE data

JunosOperating system

Affected:= 17.3= 17.4= 18.1= 18.2= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1= 20.2

Junos Os EvolvedOperating system

Affected:= 20.3

CVSS breakdown

From the vector

Attack vector: Network
Complexity: Low
Privileges: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected?

dbcve checks

Work through these to decide whether this CVE applies to you.

Identify Junos OS version

Run 'show version' or 'system version' command to display the installed Junos OS version

Affected if Version matches any of these: 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2 (Junos) or 20.3 (Junos OS Evolved)
Confirm BGP protocol is enabled

Run 'show bgp summary' or check configuration with 'show configuration protocols bgp' to see if BGP is configured

Affected if BGP is actively configured (either IBGP or EBGP) on the device
Verify RPD daemon status

Run 'show routing daemon' or check system processes to confirm the rpd (routing process daemon) is running

Affected if RPD is running and handling BGP sessions
Check for recent RPD crashes or restarts

Review system logs with 'show log messages' or 'show system processes extensive' looking for rpd crash or restart entries

Affected if RPD has recently crashed or restarted, especially in correlation with BGP traffic patterns

The device is affected if it runs a vulnerable Junos version (17.3-20.2 for Junos, 20.3 for Junos OS Evolved) AND has BGP protocol enabled, with the vulnerability triggered by receipt of specially crafted BGP UPDATE or KEEPALIVE messages.

Generated from the published advisory. Verify against your own configuration.

Remediation

dbcve · scoped

Mitigation available No clean upgrade yet — mitigate in the meantime

Mitigation

Apply the vendor-supplied patches or upgrade to a fixed Junos OS version as listed in the Juniper Networks advisory. Consider implementing BGP traffic filtering or rate limiting as a temporary workaround while planning the upgrade.

Recommended fix High confidence

Upgrade to the appropriate fixed release for your version branch (e.g., 17.3R3-S11, 17.4R3-S4, 18.2R3-S7, 20.3R2, or later stable releases)

1. Identify the current Junos OS or Junos OS Evolved version installed using 'show version' command
2. Review the Juniper Security Bulletin (kb.juniper.net) for this CVE to confirm the exact fixed version for your specific Junos release train
3. Plan maintenance window as upgrade will require device reboot
4. Backup current configuration using 'request system configuration rescue save'
5. Download the appropriate fixed Junos version from Juniper Networks (e.g., 17.3R3-S11, 17.4R3-S4, 18.2R3-S7, or later)
6. Upload the Junos upgrade package to the device using FTP/SCP
7. Install the upgrade using 'request system software add <package-name>' command
8. Reboot the device using 'request system reboot' command

Caveat Standard Junos upgrade may cause brief routing disruption during reboot; ensure redundancy if high availability is required

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Junos Scoped from the published advisory

Consultation4.0 h
Implementation8.0 h
Testing4.0 h
Review / QA2.0 h

18.0 hours of engineering $3,200

Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,120.

Scan for this in your stack

Free · runs locally

dbcve dependency scanner

Check whether your project pulls in CVE-2021-31374 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References

Primary sources

kb.juniper.netVendor Advisory
nvd.nist.govNVD record

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-31374 in production — separate from our analysis above.

Notes0 Guidelines

Know something about CVE-2021-31374?

The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.

The version that genuinely resolved it — not the one the vendor claimed
A config change or rule that shut the vector down
A gotcha in the upgrade path that cost you an afternoon

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here

Verified mitigations, workarounds, and config changes
Version or environment caveats, and links to real fixes
No weaponised exploit code, or anything meant to cause harm
No spam, self-promotion, credentials, or personal data

At a glance

A fix existsA vendor remedy is published

Severity 7.5 High

Exploit likelihood EPSS, next 30 days 1.0%

Affects: Junos

Remediation

A high-priority fix

Fix this in Junos 18 hrs · High

Typical engagement from $3,200

Get a fix See the full breakdown ↓

A high-priority vulnerability. Send your environment and a specialist will scope CVE-2021-31374 and return a fixed quote and timeline.

You’ll deal with our team directly and deploy the reviewed fix to staging first — never straight to production.

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

Check your environment

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

Scan for this in your stack

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Practitioner notes

No notes yet

Official description

Technical summary

Affected products & versions

CVSS breakdown

Am I affected?

Remediation

References