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

published 2021-01-15 5y ago modified 2026-06-17 4mo ago also EUVD-2021-2824

cvss: 5.8; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 1.2%; EPSS 1.2% chance of exploitation in 30 days, percentile 68%
public exploits: 0; none known

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;

Patch / fix

fixed in 1

Juniper Networks 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

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Exploit prediction

1.22% chance of exploitation in the next 30 days, higher than 68% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by	version	score	vector
CNA	3.1	5.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L
NVD	2.0	4.3	AV:N/AC:M/Au:N/C:N/I:N/A:P

Affected products

Juniper Networks Junos OS

Classification

Weakness

CWE-284 Improper Access Control

References

kb.juniper.net /JSA11095
vendor-advisory

Sources

CVE List CVE-2021-0205
NVD CVE-2021-0205

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