Security readout for executives and security teams
Plain-English summary
This Junos OS Evolved flaw can let a nearby network attacker disrupt switching behavior by triggering management-interface instability. The impact is operational: new MAC learning over label-switched interfaces can stop, logs can flood, and CPU use can rise. It is not described as data theft or remote device takeover, but it can affect availability on exposed network infrastructure.
Executive priority
Treat as a high-priority network availability issue for Junos OS Evolved environments, especially where label-switched interfaces support critical services. Schedule remediation through normal emergency or accelerated network maintenance processes. Risk is lower where adjacent management-plane access is tightly restricted, but affected versions should still be upgraded.
Technical view
CVE-2026-21911 is a CWE-682 incorrect calculation issue in Junos OS Evolved l2cpd. An unauthenticated network-adjacent attacker can cause management-interface flapping that stops new MAC learning over label-switched interfaces and generates repeated error logs, causing high CPU usage. CVSS v4.0 is 7.1 with adjacent attack vector, low complexity, no privileges, and high vulnerable-system availability impact.
Likely exposure
Exposure is limited to Juniper Networks devices running affected Junos OS Evolved releases with reachable adjacent network access to the management interface path. Organizations using label-switched interfaces should prioritize review because the described failure affects MAC learning and control-plane resource consumption.
Exploitation context
The source bundle does not indicate public exploitation or CISA KEV listing. Exploitation requires network-adjacent positioning, not internet-wide remote access. The reported outcome is denial-of-service style disruption: MAC learning stops on LSI and log volume plus CPU load increases.
Researcher notes
Evidence is limited to the CVE record and Juniper advisory references in the source bundle. No exploit code, public exploitation, or workaround details are provided. The affected ranges are explicit, but validation should rely on actual device software versions and Juniper’s JSA106010 for authoritative remediation details.
Mitigation direction
- Upgrade to a Junos OS Evolved release listed as not vulnerable in Juniper guidance.
- Prioritize fixed trains: 21.4R3-S7-EVO, 22.2R3-S4-EVO, 22.3R3-S3-EVO, or later.
- For 22.4, move to 22.4R3-S2-EVO or later per the advisory.
- For 23.2, move to 23.2R2-S1-EVO or later per the advisory.
- For 23.4, move to 23.4R1-S2-EVO, 23.4R2-EVO, or later.
- Review Juniper advisory JSA106010 for any platform-specific operational guidance.
Validation and detection
- Inventory Junos OS Evolved versions across Juniper infrastructure.
- Compare installed versions against the affected and fixed release ranges in JSA106010.
- Check logs for the advisory’s GETIFBD_VALIDATE_FAILED and IFBD_VALIDATE_FAIL_EPOCH_MISMATCH message pattern.
- Monitor affected devices for abnormal l2cpd logging and elevated CPU usage.
- Confirm whether label-switched interfaces are deployed on potentially affected devices.
- After upgrade, verify MAC learning resumes normally and log flooding stops.
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-682: 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-2026-21911 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
- High
- CVSS
- 7.1 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/V:C/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:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/V:C/RE:M/U:Amber——Primary CVE scoreVulnerability scoring details
Base CVSS 4.0 score
7.1HighVector: CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/V:C/RE:M/U:Amber
Source materials
- CVE List V5 sourceCVE List V5
- https://supportportal.juniper.net/JSA106010CVE reference · vendor-advisory
- https://kb.juniper.net/JSA106010CVE 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.
Incorrect Calculation
Incorrect Calculation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.