CVE-2026-21909

RPD crash via IS-IS packet memory leak

Published Jan 15, 2026 · Updated Jan 15, 2026

Memory leak in the rpd daemon in Juniper Networks Junos OS and Junos OS Evolved allows attackers to crash rpd with an IS-IS update. Rpd fails to release memory after processing a specific IS-IS update packet, so repeated packets consume all available memory. Exploitation requires control of an adjacent IS-IS neighbor and interrupts routing-protocol service when rpd crashes.

CVSS severity7.1
High
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory leak in the rpd daemon in Juniper Networks Junos OS and Junos OS Evolved allows attackers to crash rpd with an IS-IS update. Rpd fails to release memory after processing a specific IS-IS update packet, so repeated packets consume all available memory. Exploitation requires control of an adjacent IS-IS neighbor and interrupts routing-protocol service when rpd crashes.

The record

CVE
CVE-2026-21909
Published
Jan 15, 2026
Updated
Jan 15, 2026
Vendor
Juniper Networks
Product
Junos OS Evolved
Classifications
CWE-401, T1499.004
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 15, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 15, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=23.2 <23.2R2-EVO
  2. Affected versionversion=23.4 <23.4R1-S2-EVO, 23.4R2-EVO
  3. Affected versionversion=24.1 <24.1R2-EVO

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OS Evolvedversion=23.2 <23.2R2-EVO; version=23.4 <23.4R1-S2-EVO, 23.4R2-EVO; version=24.1 <24.1R2-EVO
Juniper Networks · Junos OSversion=23.2 <23.2R2; version=23.4 <23.4R1-S2, 23.4R2; version=24.1 <24.1R2

Published CVSS scores

7.1Juniper Networks, Inc.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
6.5Juniper Networks, Inc.CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-401Missing Release of Memory after Effective Lifetime
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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