CVE-2021-0221

Packet-processing denial of service via multicast loop

Published Jan 15, 2021 · Updated Sep 16, 2024

Improper exceptional-condition handling in Junos OS on QFX Series allows remote attackers to interrupt packet processing via IP multicast. On an EVPN/VXLAN provider edge with an IRB virtual gateway address, specific multicast traffic enters a forwarding loop instead of terminating. The affected configuration and local-network reachability are required; the loop drives abnormal interface traffic and denies packet processing.

CVSS severity6.5
Medium
EPSS probability0.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper exceptional-condition handling in Junos OS on QFX Series allows remote attackers to interrupt packet processing via IP multicast. On an EVPN/VXLAN provider edge with an IRB virtual gateway address, specific multicast traffic enters a forwarding loop instead of terminating. The affected configuration and local-network reachability are required; the loop drives abnormal interface traffic and denies packet processing.

The record

CVE
CVE-2021-0221
Published
Jan 15, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-703, CWE-835, T1499.002
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 15, 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=17.4 <17.4R2-S12, 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 <18.4R2-S5, 18.4R3-S5
  6. Affected versionversion=19.1 <19.1R1-S6, 19.1R2-S2, 19.1R3-S3
  7. Affected versionversion=19.2 <19.2R1-S5, 19.2R3-S1
  8. Affected versionversion=19.3 <19.3R2-S5, 19.3R3
  9. Affected versionversion=19.4 <19.4R2-S2, 19.4R3
  10. Affected versionversion=20.1 <20.1R2
  11. Affected versionversion=20.2 <20.2R1-S2, 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 <17.4R2-S12, 17.4R3-S3; version=18.1 <18.1R3-S11; version=18.2 <18.2R3-S6; version=18.3 <18.3R3-S4; version=18.4 <18.4R2-S5, 18.4R3-S5; version=19.1 <19.1R1-S6, 19.1R2-S2, 19.1R3-S3; version=19.2 <19.2R1-S5, 19.2R3-S1; version=19.3 <19.3R2-S5, 19.3R3; version=19.4 <19.4R2-S2, 19.4R3; version=20.1 <20.1R2; version=20.2 <20.2R1-S2, 20.2R2; version=unspecified <17.3R3-S10

Published CVSS scores

2.9NISTAV:A/AC:M/Au:N/C:N/I:N/A:P
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 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-703Improper Check or Handling of Exceptional Conditions
CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.002Service Exhaustion

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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