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JunosOperating system · Juniper

CVE-2021-0216

MEDIUM · 6.5 CVSS v3.1 Published 2021-04-22
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
70/100
Remediation priority · Elevated
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
A vulnerability in Juniper Networks Junos OS running on the ACX5448 and ACX710 platforms may cause BFD sessions to flap when a high rate of transit ARP packets are received. This, in turn, may impact routing protocols and network stability, leading to a Denial of Service (DoS) condition. When a high rate of transit ARP packets are exceptioned to the CPU and BFD flaps, the following log messages may be seen: bfdd[15864]: BFDD_STATE_UP_TO_DOWN: BFD Session 192.168.14.3 (IFL 232) state Up -> Down LD/RD(17/19) Up time:11:38:17 Local diag: CtlExpire Remote diag: None Reason: Detect Timer Expiry. bfdd[15864]: BFDD_TRAP_SHOP_STATE_DOWN: local discriminator: 17, new state: down, interface: irb.998, peer addr: 192.168.14.3 rpd[15839]: RPD_ISIS_ADJDOWN: IS-IS lost L2 adjacency to peer on irb.998, reason: BFD Session Down bfdd[15864]: BFDD_TRAP_SHOP_STATE_UP: local discriminator: 17, new state: up, interface: irb.998, peer addr: 192.168.14.3 This issue only affects the ACX5448 Series and ACX710 Series routers. No other products or platforms are affected by this vulnerability. This issue affects Juniper Networks Junos OS: 18.2 versions prior to 18.2R3-S8 on ACX5448; 18.3 versions prior to 18.3R3-S5 on ACX5448; 18.4 versions prior to 18.4R1-S6, 18.4R3-S7 on ACX5448; 19.1 versions prior to 19.1R3-S5 on ACX5448; 19.2 versions prior to 19.2R2, 19.2R3 on ACX5448; 19.3 versions prior to 19.3R3 on ACX5448; 19.4 versions prior to 19.4R3 on ACX5448; 20.1 versions prior to 20.1R2 on ACX5448; 20.2 versions prior to 20.2R2 on ACX5448 and ACX710.

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

A vulnerability in Juniper Networks Junos OS on ACX5448 and ACX710 platforms causes BFD (Bidirectional Forwarding Detection) sessions to flap when the device receives a high rate of transit ARP packets that get exceptioned to the CPU. This BFD session instability can cause routing protocols like IS-IS to lose adjacencies, resulting in a Denial of Service condition.

MitigationUpgrade Junos OS to the specified patched versions: 18.2R3-S8 or later, 18.3R3-S5 or later, 18.4R1-S6/18.4R3-S7 or later, 19.1R3-S5 or later, 19.2R2/19.2R3 or later, 19.3R3 or later, 19.4R3 or later, 20.1R2 or later, or 20.2R2 or later depending on the platform.

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:= 20.2= 18.2= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1

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
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:A/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. Confirm device model is ACX5448 or ACX710
    Run 'show chassis hardware' or 'show system information' to identify the hardware platform
    Affected if The device is not an ACX5448 or ACX710 platform (this CVE only affects those specific models)
  2. Check installed Junos OS version
    Run 'show version' and compare the firmware version against the affected ranges: 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, or 20.2
    Affected if The installed Junos version matches one of the listed affected versions
  3. Verify BFD is configured and active
    Run 'show bfd session' to see if any BFD sessions exist
    Affected if BFD sessions are configured and active on the device
  4. Look for BFD session instability
    Run 'show bfd session extensive' repeatedly over time or check 'show bfd session history' for session flaps
    Affected if BFD sessions are showing frequent flapping or down transitions, especially correlating with high ARP traffic to CPU

The device is affected if it is an ACX5448 or ACX710 running a vulnerable Junos version (18.2-20.2) and BFD sessions are exhibiting unexpected flapping behavior.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Junos OS to the specified patched versions: 18.2R3-S8 or later, 18.3R3-S5 or later, 18.4R1-S6/18.4R3-S7 or later, 19.1R3-S5 or later, 19.2R2/19.2R3 or later, 19.3R3 or later, 19.4R3 or later, 20.1R2 or later, or 20.2R2 or later depending on the platform.

Fix this in Junos Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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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-2021-0216 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
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