CVE-2026-21903Network attack vector

FPC crash via scaled telemetry subscriptions

Published Jan 15, 2026 · Updated Jan 15, 2026

Stack buffer overflow in affected Junos OS releases allows remote authenticated users to crash and restart FPCs via telemetry subscriptions. At scale, sensor subscriptions overflow a Packet Forwarding Engine stack buffer and drop all FPC connections, forcing the FPCs to restart. Low-privilege network access to telemetry is sufficient; the failure was not observed when the relevant sensor YANG packages were installed.

CVSS severity7.1
High
EPSS probability0.40%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack buffer overflow in affected Junos OS releases allows remote authenticated users to crash and restart FPCs via telemetry subscriptions. At scale, sensor subscriptions overflow a Packet Forwarding Engine stack buffer and drop all FPC connections, forcing the FPCs to restart. Low-privilege network access to telemetry is sufficient; the failure was not observed when the relevant sensor YANG packages were installed.

The record

CVE
CVE-2026-21903
Published
Jan 15, 2026
Updated
Jan 15, 2026
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-121, T1499.004
Attack vector
network
Privileges
authenticated

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=0 <22.4R3-S7
  2. Affected versionversion=23.2 <23.2R2-S4
  3. Affected versionversion=23.4 <23.4R2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Juniper Networks · Junos OSversion=0 <22.4R3-S7; version=23.2 <23.2R2-S4; version=23.4 <23.4R2

Published CVSS scores

7.1Juniper Networks, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L
6.5Juniper Networks, Inc.CVSS:3.1/AV:N/AC:L/PR:L/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-121Stack-based Buffer Overflow
T1499.004Endpoint Denial of Service: Application 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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