CVE-2021-0271

Sustained service interruption via double-free ARP processing

Published Apr 22, 2021 · Updated Sep 16, 2024

Double free in Junos OS sfid on affected EX Series devices allows attackers on an adjacent network to crash the process with a crafted ARP packet. The sfid process frees the same allocation twice while processing the packet; Juniper has not disclosed the responsible function or field. Reachability requires Layer 2 adjacency and a listed Marvell-chipset EX Series device; repeated packets sustain the outage by repeatedly crashing sfid.

CVSS severity6.5
Medium
EPSS probability0.40%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Double free in Junos OS sfid on affected EX Series devices allows attackers on an adjacent network to crash the process with a crafted ARP packet. The sfid process frees the same allocation twice while processing the packet; Juniper has not disclosed the responsible function or field. Reachability requires Layer 2 adjacency and a listed Marvell-chipset EX Series device; repeated packets sustain the outage by repeatedly crashing sfid.

The record

CVE
CVE-2021-0271
Published
Apr 22, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-415, T1499.004
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=12.3 <12.3R12-S17
  2. Affected versionversion=15.1 <15.1R7-S8

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=12.3 <12.3R12-S17; version=15.1 <15.1R7-S8

Published CVSS scores

6.5Juniper NetworksCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-415Double Free
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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