Security readout for executives and security teams
Plain-English summary
CVE-2026-21912 can let a low-privileged local user disrupt certain Juniper MX10k routers. On systems with LC480 or LC2101 line cards, repeated use of a firmware-status CLI command may reset a line card and later restart chassisd, causing service disruption and core dumps.
Executive priority
Treat as a maintenance-priority availability risk for core routing environments. It is not remotely exploitable per the provided data, but a compromised or misused low-privileged account could disrupt important network services.
Technical view
Juniper describes a TOCTOU race condition in Junos OS when collecting FPC Ethernet firmware statistics. The issue is limited to MX10k Series systems with LC480 or LC2101 line cards. A local low-privileged attacker can trigger line card crash/restart behavior, with possible later chassisd crash/restart.
Likely exposure
Exposure is likely limited to Juniper MX10k Series routers using LC480 or LC2101 line cards and affected Junos OS releases before the fixed trains listed by Juniper. Other platforms or line cards are not identified as affected in the provided sources.
Exploitation context
Attack requires authenticated local CLI access with low privileges. The provided sources and KEV status do not indicate active exploitation. The main risk is availability loss on high-value routing infrastructure, especially if low-privileged accounts are broadly assigned or compromised.
Researcher notes
Evidence is from CVE and Juniper advisory references. No public exploit activity is cited, and KEV is false. Scope appears narrowly tied to MX10k with LC480 or LC2101 line cards. Validate exact fixes and any operational caveats directly in JSA106011.
Mitigation direction
- Upgrade affected MX10k systems to the fixed Junos OS releases listed in Juniper advisory JSA106011.
- Restrict low-privileged CLI access to trusted administrators until remediation is complete.
- Review vendor advisory JSA106011 for any updated workaround or operational guidance.
- Prioritize routers carrying critical production or customer traffic.
Validation and detection
- Inventory MX10k routers and identify LC480 or LC2101 line cards.
- Compare installed Junos OS versions against Juniper’s affected and fixed release ranges.
- Review logs for line card resets, chassisd restarts, or related core dumps.
- Audit which accounts can access operational CLI commands on affected routers.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-367: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-21912 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 6.8 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/RE:M/U:Amber
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/RE:M/U:Amber——Primary CVE scoreVulnerability scoring details
Base CVSS 4.0 score
6.8MediumVector: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/RE:M/U:Amber
Source materials
- CVE List V5 sourceCVE List V5
- https://supportportal.juniper.net/JSA106011CVE reference · vendor-advisory
- https://kb.juniper.net/JSA106011CVE reference · vendor-advisory
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Time-of-check Time-of-use (TOCTOU) Race Condition
Time-of-check Time-of-use (TOCTOU) Race Condition represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.