Juniper Junos OS up to 24.2R1 on MX10k FPC Ethernet Firmware Statistics toctou

Summaryinfo

A vulnerability was found in Juniper Junos OS up to 24.2R1 on MX10k. It has been rated as problematic. Impacted is an unknown function of the component FPC Ethernet Firmware Statistics. This manipulation causes toctou. This vulnerability is tracked as CVE-2026-21912. The attack is restricted to local execution. No exploit exists. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Juniper Junos OS up to 24.2R1 on MX10k. It has been declared as problematic. Affected by this vulnerability is an unknown function of the component FPC Ethernet Firmware Statistics. The manipulation with an unknown input leads to a toctou vulnerability. The CWE definition for the vulnerability is CWE-367. The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. This can cause the product to perform invalid actions when the resource is in an unexpected state. As an impact it is known to affect availability. The summary by CVE is:

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 22.2 before 22.2R3-S7,  * from 22.4 before 22.4R3-S6,  * from 23.2 before 23.2R2-S2,  * from 23.4 before 23.4R2-S3,  * from 24.2 before 24.2R2.

It is possible to read the advisory at supportportal.juniper.net. This vulnerability is known as CVE-2026-21912 since 01/05/2026. The exploitation appears to be easy. Attacking locally is a requirement. The technical details are unknown and an exploit is not publicly available.

Upgrading to version 21.2R3-S10, 21.4R3-S9, 22.2R3-S7, 22.4R3-S6, 23.2R2-S2, 23.4R2-S3 or 24.2R2 eliminates this vulnerability.

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Productinfo

Type

• Router Operating System

Vendor

• Juniper

Name

• Junos OS

Version

• 21.4R3-S8
• 22.2R3-S6
• 22.4R3-S5
• 23.2R2-S1
• 23.4R2-S2
• 24.2R1

License

• commercial

Website

• Vendor: https://www.juniper.net/

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CPE 2.2info

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