CVE-2021-0243

Limited service interruption via failed policer discard

Published Apr 22, 2021 · Updated Sep 17, 2024

Improper data handling in the Junos OS firewall policer on EX4300 switches allows remote attackers on an adjacent network to interrupt service. When an IPv4 stateless policer with a discard action is applied to a Layer 2 port, matching traffic above its limit is forwarded instead of discarded. Exploitation requires the affected policer configuration; IPv6 traffic and other firewall policing actions are unaffected.

CVSS severity4.7
Medium
EPSS probability0.38%
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

Improper data handling in the Junos OS firewall policer on EX4300 switches allows remote attackers on an adjacent network to interrupt service. When an IPv4 stateless policer with a discard action is applied to a Layer 2 port, matching traffic above its limit is forwarded instead of discarded. Exploitation requires the affected policer configuration; IPv6 traffic and other firewall policing actions are unaffected.

The record

CVE
CVE-2021-0243
Published
Apr 22, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-241, T1498.001
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 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=17.4 <17.4R3-S3
  2. Affected versionversion=18.1 <18.1R3-S11
  3. Affected versionversion=18.2 <18.2R3-S6
  4. Affected versionversion=18.3 <18.3R3-S4
  5. Affected versionversion=18.4 <18.4R3-S6
  6. Affected versionversion=19.1 <19.1R3-S3
  7. Affected versionversion=19.2 <19.2R3-S1
  8. Affected versionversion=19.3 <19.3R3-S1
  9. Affected versionversion=19.4 <19.4R3
  10. Affected versionversion=20.1 <20.1R2
  11. Affected versionversion=20.2 <20.2R2
  12. Affected versionversion=unspecified <17.3R3-S10

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=17.4 <17.4R3-S3; version=18.1 <18.1R3-S11; version=18.2 <18.2R3-S6; version=18.3 <18.3R3-S4; version=18.4 <18.4R3-S6; version=19.1 <19.1R3-S3; version=19.2 <19.2R3-S1; version=19.3 <19.3R3-S1; version=19.4 <19.4R3; version=20.1 <20.1R2; version=20.2 <20.2R2; version=unspecified <17.3R3-S10

Published CVSS scores

3.3NIST NVDAV:A/AC:L/Au:N/C:N/I:N/A:P
4.7Juniper NetworksCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L

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-241Improper Handling of Unexpected Data Type
T1498.001Direct Network Flood

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