Junos OS: MX Series: Dynamic filter fails to match IPv6 prefix

Description

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;

Scores

EPSS (exploitation in 30 days)

1.2% · top 31% of all CVEs (7 Nov 2026)

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.8.

Weakness

• CWE-284 Improper Access Control (opens in a new tab)All about CWE-284 and its CVEs

Affected products

• Juniper Networks · Junos OS

  • affected 17.3 – < 17.3R3-S10
  • affected 17.4 – < 17.4R3-S3
  • affected 18.1 – < 18.1R3-S11
  • affected 18.2 – < 18.2R3-S6
  • affected 18.3 – < 18.3R3-S4
  • affected 18.4 – < 18.4R3-S6
  • affected 19.1 – < 19.1R2-S2, 19.1R3-S3
  • affected 19.2 – < 19.2R3-S1
  • affected 19.3 – < 19.3R2-S5, 19.3R3-S1
  • affected 19.4 – < 19.4R3
  • affected 20.1 – < 20.1R2
  • affected 20.2 – < 20.2R2

What to do

Solution: 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.

Workaround: IDS configuration can be disabled.

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

References (1)

• https://kb.juniper.net/JSA11095 (opens in a new tab)x_refsource_CONFIRMx_transferred

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2021-0205](https://trackcve.app/badge/CVE-2021-0205.svg)](https://trackcve.app/cve/CVE-2021-0205)

Record last updated 16 Sept 2024, 17:28 UTC.