Medium [CVE-2026-21912] Junos: Time-of-check Time-of-use (TOCTOU) Race Condition vulnerability in the method to collect FPC Ethernet firmware statistics of…
This medium-severity Juniper Networks advisory covers CVE-2026-21912 affecting Junos, Junos OS, MX.
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Summary
A Time-of-check Time-of-use (TOCTOU) Race Condition vulnerability in the method to collect FPC Ethernet firmware statistics of Juniper Networks Junos OS on MX10k Series allows a local, low-privileged attacker executing the 'show system firmware' CLI command to cause an LC480 or LC2101 line card to reset.
On MX10k Series systems with LC480 or LC2101 line cards, repeated execution of the 'show system firmware' CLI command can cause the line card to crash and restart. Additionally, some time after the line card crashes, chassisd may also crash and restart, generating a core dump.
This issue affects Junos OS on MX10k Series:
- all versions before 21.2R3-S10,
- from 21.4 before 21.4R3-S9,
- from 23.2 before 23.2R2-S2,
- from 23.4 before 23.4R2-S3,
Affected products named by the advisory: MX; EX.
- 21.4
- 22.2
- 22.4
- 23.2
- 23.4
- 24.2
- all versions
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
- 21.2R3-S10
- 21.4R3-S9
- 22.2R3-S7
- 22.4R3-S6
- 23.2R2-S2
- 23.4R2-S3
- 24.2R2
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
Mitigation
Upgrade to a fixed release: 21.2R3-S10, 21.4R3-S9, 22.2R3-S7, 22.4R3-S6, 23.2R2-S2, 23.4R2-S3. That is the remediation for this advisory.
The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
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