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2021-01 Security Bulletin: Junos OS: MX Series: Dynamic filter fails to match IPv6 prefix (CVE-2021-0205)



Article ID: JSA11095 SECURITY_ADVISORIES Last Updated: 13 Jan 2021Version: 1.0
Product Affected:
This issue affects Junos OS 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2. Affected platforms: MX Series.

When the "Intrusion Detection Service" (IDS) feature is configured on Juniper Networks MX series with a dynamic firewall filter using IPv6 source or destination prefix, it may incorrectly match the prefix as /32, causing the filter to block unexpected traffic.

This issue affects only IPv6 prefixes when used as source and destination.

This issue affects MX Series devices using MS-MPC, MS-MIC or MS-SPC3 service cards with IDS service configured.

This issue affects Juniper Networks Junos OS:

  • 17.3 versions prior to 17.3R3-S10 on MX Series;
  • 17.4 versions prior to 17.4R3-S3 on MX Series;
  • 18.1 versions prior to 18.1R3-S11 on MX Series;
  • 18.2 versions prior to 18.2R3-S6 on MX Series;
  • 18.3 versions prior to 18.3R3-S4 on MX Series;
  • 18.4 versions prior to 18.4R3-S6 on MX Series;
  • 19.1 versions prior to 19.1R2-S2, 19.1R3-S3 on MX Series;
  • 19.2 versions prior to 19.2R3-S1 on MX Series;
  • 19.3 versions prior to 19.3R2-S5, 19.3R3-S1 on MX Series;
  • 19.4 versions prior to 19.4R3 on MX Series;
  • 20.1 versions prior to 20.1R2 on MX Series;
  • 20.2 versions prior to 20.2R2 on MX Series;

The example of the configuration stanza affected by this issue is as follows:

[services ids]

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

This issue was seen during production usage.

This issue has been assigned CVE-2021-0205.


The following software releases have been updated to resolve this specific issue: Junos OS 17.3R3-S10, 17.4R3-S3, 18.1R3-S11, 18.2R3-S6, 18.3R3-S4, 18.4R3-S6, 19.1R2-S2, 19.1R3-S3, 19.2R3-S1, 19.3R2-S5, 19.3R3-S1, 19.4R3, 20.1R2, 20.2R2, 20.3R1 and all subsequent releases.

This issue is being tracked as 1536100.


IDS configuration can be disabled.

Software releases or updates are available for download at
Modification History:
2021-01-13: Initial Publication.
CVSS Score:
5.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L)
Severity Level:
Severity Assessment:
Information for how Juniper Networks uses CVSS can be found at KB 16446 "Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories."

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