CVE-2021-0239

PFE denial of service via Layer 2 frames

Published Apr 22, 2021 · Updated Sep 16, 2024

Improper exception handling in Junos OS Evolved before 20.4R1-EVO allows remote attackers to cause denial of service via Layer 2 frames. The Evo-aftmand Advanced Forwarding Toolkit manager mishandles a stream of specific genuine Layer 2 frames, crashes, and restarts inside the packet forwarding engine. An unauthenticated adjacent attacker can repeat the stream to repeatedly crash the PFE and sustain traffic disruption; Junos OS versions are not affected.

CVSS severity6.5
Medium
EPSS probability0.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper exception handling in Junos OS Evolved before 20.4R1-EVO allows remote attackers to cause denial of service via Layer 2 frames. The Evo-aftmand Advanced Forwarding Toolkit manager mishandles a stream of specific genuine Layer 2 frames, crashes, and restarts inside the packet forwarding engine. An unauthenticated adjacent attacker can repeat the stream to repeatedly crash the PFE and sustain traffic disruption; Junos OS versions are not affected.

The record

CVE
CVE-2021-0239
Published
Apr 22, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS Evolved
Classifications
CWE-754, T1499.001
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=unspecified <20.4R1-EVO

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OS Evolvedversion=unspecified <20.4R1-EVO

Published CVSS scores

6.1NVDAV:A/AC:L/Au:N/C:N/I:N/A:C
6.5NVDCVSS: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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-754Improper Check for Unusual or Exceptional Conditions
T1499.001Endpoint Denial of Service

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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