CVE-2026-21912

Line-card reset via firmware-statistics TOCTOU race

Published Jan 15, 2026 · Updated Jan 15, 2026

TOCTOU race in Junos OS on MX10k Series allows local users to reset LC480 or LC2101 line cards through a firmware-status command. Juniper identifies the flaw in the FPC Ethernet firmware-statistics collection method but has not disclosed the checked resource or stale-use operation. Low-privileged CLI access is sufficient; chassisd can later crash and restart with a core dump, extending the service interruption beyond the line card.

CVSS severity6.8
Medium
EPSS probability0.11%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

TOCTOU race in Junos OS on MX10k Series allows local users to reset LC480 or LC2101 line cards through a firmware-status command. Juniper identifies the flaw in the FPC Ethernet firmware-statistics collection method but has not disclosed the checked resource or stale-use operation. Low-privileged CLI access is sufficient; chassisd can later crash and restart with a core dump, extending the service interruption beyond the line card.

The record

CVE
CVE-2026-21912
Published
Jan 15, 2026
Updated
Jan 15, 2026
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-367, CAPEC-29, T1499.004
Attack vector
local
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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=0 <21.2R3-S10
  2. Affected versionversion=21.4 <21.4R3-S9
  3. Affected versionversion=22.2 <22.2R3-S7
  4. Affected versionversion=22.4 <22.4R3-S6
  5. Affected versionversion=23.2 <23.2R2-S2
  6. Affected versionversion=23.4 <23.4R2-S3
  7. Affected versionversion=24.2 <24.2R2

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Juniper Networks · Junos OSversion=0 <21.2R3-S10; version=21.4 <21.4R3-S9; version=22.2 <22.2R3-S7; version=22.4 <22.4R3-S6; version=23.2 <23.2R2-S2; version=23.4 <23.4R2-S3; version=24.2 <24.2R2

Published CVSS scores

6.8Juniper NetworksCVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L
5.5Juniper NetworksCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.7NIST NVDCVSS:3.1/AV:L/AC:H/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)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-367Time-of-check Time-of-use (TOCTOU) Race Condition
CAPEC-29Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions
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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