CVE-2021-0205Network attack vector

IPv6 traffic interruption via /32 prefix mismatch

Published Jan 15, 2021 · Updated Sep 16, 2024

Improper access control in Juniper Networks Junos OS allows remote attackers to interrupt IPv6 traffic through an IDS dynamic filter. When a generated dynamic filter processes an IPv6 source or destination prefix, it incorrectly uses a /32 match and drops traffic outside the intended prefix. Exposure requires IDS on an MX Series router with an MS-MPC, MS-MIC, or MS-SPC3 service card and an IPv6 aggregation prefix; the consequence is unintended traffic interruption.

CVSS severity5.8
Medium
EPSS probability1.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in Juniper Networks Junos OS allows remote attackers to interrupt IPv6 traffic through an IDS dynamic filter. When a generated dynamic filter processes an IPv6 source or destination prefix, it incorrectly uses a /32 match and drops traffic outside the intended prefix. Exposure requires IDS on an MX Series router with an MS-MPC, MS-MIC, or MS-SPC3 service card and an IPv6 aggregation prefix; the consequence is unintended traffic interruption.

The record

CVE
CVE-2021-0205
Published
Jan 15, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-284, T1498
Attack vector
network
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

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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=17.3 <17.3R3-S10
  2. Affected versionversion=17.4 <17.4R3-S3
  3. Affected versionversion=18.1 <18.1R3-S11
  4. Affected versionversion=18.2 <18.2R3-S6
  5. Affected versionversion=18.3 <18.3R3-S4
  6. Affected versionversion=18.4 <18.4R3-S6
  7. Affected versionversion=19.1 <19.1R2-S2, 19.1R3-S3
  8. Affected versionversion=19.2 <19.2R3-S1
  9. Affected versionversion=19.3 <19.3R2-S5, 19.3R3-S1
  10. Affected versionversion=19.4 <19.4R3
  11. Affected versionversion=20.1 <20.1R2
  12. Affected versionversion=20.2 <20.2R2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=17.3 <17.3R3-S10; version=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 <19.1R2-S2, 19.1R3-S3; version=19.2 <19.2R3-S1; version=19.3 <19.3R2-S5, 19.3R3-S1; version=19.4 <19.4R3; version=20.1 <20.1R2; version=20.2 <20.2R2

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:P
5.8Juniper Networks, Inc.CVSS:3.1/AV:N/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 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-284Improper Access Control
T1498Network Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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