CVE-2021-0271
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 · uneditedA Double Free vulnerability in the software forwarding interface daemon (sfid) process of Juniper Networks Junos OS allows an adjacently-connected attacker to cause a Denial of Service (DoS) by sending a crafted ARP packet to the device. Continued receipt and processing of the crafted ARP packets will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS on EX2200-C Series, EX3200 Series, EX3300 Series, EX4200 Series, EX4500 Series, EX4550 Series, EX6210 Series, EX8208 Series, EX8216 Series. 12.3 versions prior to 12.3R12-S17; 15.1 versions prior to 15.1R7-S8. This issue only affects the listed Marvell-chipset based EX Series devices. No other products or platforms are affected.
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 confidenceA double-free vulnerability exists in the software forwarding interface daemon (sfid) process of Juniper Networks Junos OS on specific Marvell-chipset based EX Series switches. An adjacent attacker can trigger the vulnerability by sending a crafted ARP packet to the device, causing the sfid process to crash. Repeated exploitation results in a sustained Denial of Service condition as the process repeatedly crashes upon processing malicious packets.
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= 12.3= 15.1CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Identify device model and chipsetRun 'show chassis hardware' or 'show system information' to confirm the device is an EX Series switch and identify the chipset vendor (Marvell)Affected if Device is an EX Series switch with Marvell-chipset and sfid process present
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Check Junos OS versionRun 'show version' to display the installed Junos OS versionAffected if Version is 12.3 or 15.1 release family prior to the fixed releases (12.3R12-S17 or 15.1R7-S8)
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Verify sfid process is runningRun 'show system processes | match sfid' to check if the software forwarding interface daemon process is activeAffected if sfid process is running on the device
The device is affected if it is an EX Series switch with Marvell chipset running Junos OS 12.3 or 15.1, and the sfid process is active.
Generated from the published advisory. Verify against your own configuration.
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 dataUpgrade Junos OS to version 12.3R12-S17 or later for 12.3 branches, or 15.1R7-S8 or later for 15.1 branches. For interim mitigation, consider network segmentation to limit adjacent attacker access or implement ACLs to filter suspicious ARP traffic if the device supports such filtering.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-0271 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-0271 in production — separate from our analysis above.
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
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- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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