CVE-2021-0264Network attack vector

Line-card restart via syslog-action firewall filter

Published Apr 22, 2021 · Updated Sep 16, 2024

Denial of service in affected Juniper Networks Junos OS and Junos OS Evolved releases allows remote attackers to restart line cards. Packet processing fails when traffic matches a firewall filter on lo0 or a physical interface whose term uses the syslog action, crashing and restarting the line card. Exposure is limited to MX Series routers with MPC10 or MPC11 cards and PTX10003 or PTX10008 routers; repeated matching packets sustain the traffic-processing outage.

CVSS severity5.9
Medium
EPSS probability0.98%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Denial of service in affected Juniper Networks Junos OS and Junos OS Evolved releases allows remote attackers to restart line cards. Packet processing fails when traffic matches a firewall filter on lo0 or a physical interface whose term uses the syslog action, crashing and restarting the line card. Exposure is limited to MX Series routers with MPC10 or MPC11 cards and PTX10003 or PTX10008 routers; repeated matching packets sustain the traffic-processing outage.

The record

CVE
CVE-2021-0264
Published
Apr 22, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS Evolved
Classifications
CWE-703, CWE-755, T1499.004
Attack vector
network
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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=unspecified <20.4R2-EVO

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OS Evolvedversion=unspecified <20.4R2-EVO
Juniper Networks · Junos OSversion=19.3 <19.3R3-S2; version=19.4 <19.4R3-S2; version=20.1 <20.1R3; version=20.2 <20.2R2-S2, 20.2R3; version=20.3 <20.3R3; version=20.4 <20.4R2

Published CVSS scores

5.9Juniper Networks, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST National Vulnerability DatabaseAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-703Improper Check or Handling of Exceptional Conditions
CWE-755Improper Handling of Exceptional Conditions
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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo