CVE-2025-21594

CVE-2025-21594 is a high-severity vulnerability in Juniper Junos with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-754.

Key facts

Description

An Improper Check for Unusual or Exceptional Conditions vulnerability in the pfe (packet forwarding engine) of Juniper Networks Junos OS on MX Series causes a port within a pool to be blocked leading to Denial of Service (DoS). In a DS-Lite (Dual-Stack Lite) and NAT (Network Address Translation) scenario, when crafted IPv6 traffic is received and prefix-length is set to 56, the ports assigned to the user will not be freed.  Eventually, users cannot establish new connections. Affected FPC/PIC need to be manually restarted to recover. Following is the command to identify the issue:      user@host> show services nat source port-block      Host_IP                     External_IP                   Port_Block      Ports_Used/       Block_State/                                                               Range           Ports_Total       Left_Time(s)     2001::                        x.x.x.x                     58880-59391     256/256*1         Active/-       >>>>>>>>port still usedThis issue affects Junos OS on MX Series:  * from 21.2 before 21.2R3-S8,  * from 21.4 before 21.4R3-S7,  * from 22.1 before 22.1R3-S6,  * from 22.2 before 22.2R3-S4,  * from 22.3 before 22.3R3-S3,  * from 22.4 before 22.4R3-S2,  * from 23.2 before 23.2R2-S1,  * from 23.4 before 23.4R1-S2, 23.4R2. This issue does not affect versions before 20.2R1.

Frequently asked questions

What is CVE-2025-21594?
An Improper Check for Unusual or Exceptional Conditions vulnerability in the pfe (packet forwarding engine) of Juniper Networks Junos OS on MX Series causes a port within a pool to be blocked leading to Denial of Service (DoS). In a DS-Lite (Dual-Stack Lite) and NAT (Network Address Translation) scenario, when crafted IPv6 traffic is received and prefix-length is set to 56, the ports assigned to the user will not be freed.  Eventually, users cannot establish new connections. Affected FPC/PIC need to be manually restarted to recover. Following is the command to identify the issue:      user@host> show services nat source port-block      Host_IP                     External_IP                   Port_Block      Ports_Used/       Block_State/                                                               Range           Ports_Total       Left_Time(s)     2001::                        x.x.x.x                     58880-59391     256/256*1         Active/-       >>>>>>>>port still usedThis issue affects Junos OS on MX Series:  * from 21.2 before 21.2R3-S8,  * from 21.4 before 21.4R3-S7,  * from 22.1 before 22.1R3-S6,  * from 22.2 before 22.2R3-S4,  * from 22.3 before 22.3R3-S3,  * from 22.4 before 22.4R3-S2,  * from 23.2 before 23.2R2-S1,  * from 23.4 before 23.4R1-S2, 23.4R2. This issue does not affect versions before 20.2R1.
How severe is CVE-2025-21594?
CVE-2025-21594 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2025-21594 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (29th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-21594?
CVE-2025-21594 primarily affects Juniper Junos. In total, 81 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2025-21594?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2025-21594 have an EU (EUVD) identifier?
Yes. CVE-2025-21594 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-10531.
When was CVE-2025-21594 published?
CVE-2025-21594 was published on 2025-04-09 and last updated on 2026-06-17.

References

Affected products (81)

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