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Fencer Vulns
medium 6.5

CVE-2026-21909 json

Junos OS and Junos OS Evolved: Receipt of specific IS-IS update packet causes memory leak leading to RPD crash

published 2026-01-15 9 mo ago modified 2026-06-17 4 mo ago also EUVD-2026-2696

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 16%
public exploits
0
none known

Summary

A Missing Release of Memory after Effective Lifetime vulnerability in the routing protocol daemon (rpd) Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated attacker controlling an adjacent IS-IS neighbor to send a specific update packet causing a memory leak. Continued receipt and processing of these packets will exhaust all available memory, crashing rpd and creating a Denial of Service (DoS) condition.

Memory usage can be monitored through the use of the 'show task memory detail' command. For example:

user@junos> show task memory detail | match ted-infra   TED-INFRA-COOKIE           25   1072     28   1184     229

user@junos>

show task memory detail | match ted-infra   TED-INFRA-COOKIE           31   1360     34   1472     307

This issue affects:

Junos OS:

* from 23.2 before 23.2R2,  * from 23.4 before 23.4R1-S2, 23.4R2,  * from 24.1 before 24.1R2;

Junos OS Evolved:

* from 23.2 before 23.2R2-EVO,  * from 23.4 before 23.4R1-S2-EVO, 23.4R2-EVO,  * from 24.1 before 24.1R2-EVO.

This issue does not affect Junos OS versions before 23.2R1 or Junos OS Evolved versions before 23.2R1-EVO.

Patch / fix

  • Juniper Networks Junos OS 23.2R2, 23.4R1-S2, 23.4R2, 24.1R2
  • Juniper Networks Junos OS Evolved 23.2R2-EVO, 23.4R1-S2-EVO, 23.4R2-EVO, 24.1R2-EVO

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
9 mo ago

Exploit prediction

0.25% chance of exploitation in the next 30 days, higher than 16% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 4.0 7.1 CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/V:C/RE:M/U:Green
CNA 4.0 7.1 CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:Y/R:A/V:C/RE:M/U:Green

Affected products

  • Juniper Networks Junos OS
  • Juniper Networks Junos OS Evolved

Classification

Weakness
  • CWE-401 Missing Release of Memory after Effective Lifetime

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.