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JunosOperating system · Juniper

CVE-2021-31383

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 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.

NVD · unedited
In Point to MultiPoint (P2MP) scenarios within established sessions between network or adjacent neighbors the improper use of a source to destination copy write operation combined with a Stack-based Buffer Overflow on certain specific packets processed by the routing protocol daemon (RPD) of Juniper Networks Junos OS and Junos OS Evolved sent by a remote unauthenticated network attacker causes the RPD to crash causing a Denial of Service (DoS). Continued receipt and processing of these packets will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS 19.2 versions prior to 19.2R3-S2; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R1-S4, 19.4R2-S4, 19.4R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3; 20.2 versions prior to 20.2R2-S3, 20.2R3; 20.3 versions prior to 20.3R2. This issue does not affect Juniper Networks Junos OS versions prior to 19.2R1. Juniper Networks Junos OS Evolved 20.1 versions prior to 20.1R3-EVO; 20.2 versions prior to 20.2R3-EVO; 20.3 versions prior to 20.3R2-EVO.

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.

dbcve analysis · high confidence

Stack-based buffer overflow in the routing protocol daemon (RPD) of Juniper Junos OS and Junos OS Evolved, triggered by an improper source-to-destination copy operation on specific packets in Point-to-MultiPoint (P2MP) scenarios. A remote unauthenticated attacker can send specially crafted packets within established neighbor sessions to crash RPD, causing a sustained DoS condition.

MitigationApply the vendor-supplied software updates to the specific Junos OS or Junos OS Evolved versions listed in the advisory that contain the fix.

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

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.

NVD · CPE data
JunosOperating system
Affected:= 19.2= 19.3= 19.4= 20.1= 20.2= 20.3
Junos Os EvolvedOperating system
Affected:= 20.1= 20.2= 20.3

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.

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? 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.

dbcve checks

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

  1. Identify Junos version
    Run 'show version' command on the device to obtain the exact Junos OS version installed
    Affected if The installed version matches 19.2, 19.3, 19.4, 20.1, 20.2, or 20.3 (or falls within these release families)
  2. Verify if P2MP features are configured
    Run 'show configuration | match pim' and 'show configuration | match mvpn' to check if Protocol Independent Multicast (PIM) or Multicast VPN is enabled, as P2MP scenarios involve these multicast protocols
    Affected if PIM or MVPN configurations are present and active on the device
  3. Check for active neighbor sessions with multicast
    Run 'show pim neighbors' to display established PIM neighbor sessions which are required for the attack vector
    Affected if Active PIM neighbor sessions exist on any interface
  4. Inspect RPD daemon status
    Run 'show routing-daemon status' or 'show system processes routing-daemon' to check if RPD is running normally
    Affected if RPD has recently crashed or is experiencing instability (this indicates the vulnerability may have been triggered)

You are affected if your Junos version is 19.2 through 20.3 AND P2MP multicast features (PIM/MVPN) with active neighbor sessions are configured on your device.

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

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the vendor-supplied software updates to the specific Junos OS or Junos OS Evolved versions listed in the advisory that contain the fix.

Recommended fix High confidence

Upgrade to the fixed maintenance release for your current version branch (e.g., Junos OS 19.4R3-S3, 20.1R3, 20.2R3, 20.3R2 or Junos OS Evolved 20.1R3-EVO, 20.2R3-EVO, 20.3R2-EVO)

  1. 1. Identify the current Junos OS or Junos OS Evolved version running on the device using 'show version' command
  2. 2. Determine the appropriate upgrade path based on the current version branch (19.2, 19.3, 19.4, 20.1, 20.2, or 20.3)
  3. 3. For Junos OS 19.2: upgrade to 19.2R3-S2 or later
  4. 4. For Junos OS 19.3: upgrade to 19.3R2-S6, 19.3R3-S2, or later
  5. 5. For Junos OS 19.4: upgrade to 19.4R1-S4, 19.4R2-S4, 19.4R3-S3, or later
  6. 6. For Junos OS 20.1: upgrade to 20.1R2-S2, 20.1R3, or later
  7. 7. For Junos OS 20.2: upgrade to 20.2R2-S3, 20.2R3, or later
  8. 8. For Junos OS 20.3: upgrade to 20.3R2 or later
Caveat Standard Junos upgrade considerations apply - review Juniper release notes for compatibility and ensure configuration backup before upgrading

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
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-31383 in production — separate from our analysis above.

No notes yet

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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