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, specifically: 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, and from 24.2 before 24.2R2.
The vulnerability has a CVSS score of 6.8, indicating a medium severity level, and it poses a risk of high availability impact. Organizations should prioritize patching immediately to mitigate the risk associated with this vulnerability.
Given the potential impact on system availability, it is critical for organizations using affected Junos OS versions to address this vulnerability as part of their security strategy.
Vulnerability Details
The official description of CVE-2026-21912 states that a TOCTOU race condition allows local attackers to execute the 'show system firmware' command, leading to a reset of the affected line cards. The vulnerability is classified under CWE-367, indicating a race condition.
The CVSS score is 6.8, reflecting a medium severity. The affected product is Junos OS, from the vendor Juniper Networks. The vulnerability was published on January 15, 2026.
Technical Analysis
The root cause of this vulnerability is a race condition in the firmware statistics collection method. The attack vector is local, meaning an attacker must have access to the device. The attack complexity is low, and the privileges required are low, making exploitation easier.
User interaction is not required for this vulnerability. The impact on confidentiality is none, on integrity is none, but on availability, it is high, as the line card resets can disrupt network services.
Risk & Impact Analysis
Risk to organizations includes potential downtime and loss of service due to line card resets. The blast radius could affect all systems utilizing the MX10k Series with the vulnerable line cards, leading to significant operational disruptions.
Organizations should address this vulnerability within their priority patch cycle, especially in environments reliant on the stability of network operations.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The following versions of Junos OS are affected: 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, and from 24.2 before 24.2R2.
Mitigation & Remediation
Organizations should apply the available patches to mitigate this vulnerability. The patches can be found on the vendor's support portal. Additionally, implementing routine monitoring of device logs for unusual activities can help detect potential exploitation attempts.
For enhanced security, consider engaging in penetration testing to identify similar vulnerabilities.
Detection Guidance
Monitor logs for repeated execution of CLI commands that may indicate an exploitation attempt. Look for abnormal resets of line cards and core dumps in the system logs, which may signify the presence of an ongoing attack.
AppSecure Threat Intelligence Insight
The long-term significance of this vulnerability lies in its potential to disrupt network operations. Security teams should be vigilant about the patterns of exploitation that may emerge from similar vulnerabilities.
Organizations must learn from such vulnerabilities and incorporate lessons into their security practices to enhance defenses against future risks.
For further insights, organizations can refer to our penetration testing methodology and the importance of maintaining a robust vulnerability management program.
Security teams should continuously assess their environments against known vulnerabilities and ensure timely remediation efforts.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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