Security readout for executives and security teams
Plain-English summary
CVE-2021-0267 can crash Juniper Junos OS DHCP service when a vulnerable device receives a crafted DHCP packet. The business risk is service disruption, especially for broadband subscriber environments using DHCP relay active-lease query. It does not expose data or allow system takeover based on the sources.
Executive priority
Prioritize remediation for broadband or subscriber-facing Junos OS deployments using DHCP relay active-lease query. The issue is high availability risk, not data theft risk. Patch during the next urgent network maintenance window for exposed subscriber infrastructure.
Technical view
The flaw is improper input validation in JDHCPD DHCP Relay Agent active-lease query handling. An unauthenticated adjacent attacker can trigger a jdhcpd core through crafted DHCP traffic, and repeated packets can sustain denial of service. Affected Junos OS branches are 19.4, 20.1, 20.2, and 20.3 before listed fixed releases. Junos OS Evolved is not affected.
Likely exposure
Exposure is likely limited to Junos OS devices running affected versions with JDHCPD DHCP Relay Agent active-lease query configured, typically broadband subscriber sessions. The CVSS vector is adjacent network, so internet-wide remote exposure is not supported by the provided sources.
Exploitation context
The source bundle does not show CISA KEV listing or other evidence of active exploitation. Exploitation requires delivering crafted DHCP traffic to a vulnerable adjacent service path. Repeated receipt can keep the DHCP service unavailable, creating operational impact without confidentiality or integrity compromise.
Researcher notes
Focus analysis on JDHCPD active-lease query parsing and service availability. The public sources provide affected branches, fixed releases, CVSS, and configuration context, but no exploit samples, indicators, or confirmed exploitation. Avoid assuming products beyond Junos OS.
Mitigation direction
- Upgrade 19.4 to 19.4R3-S1 or later fixed guidance.
- Upgrade 20.1 to 20.1R2-S1, 20.1R3, or later fixed guidance.
- Upgrade 20.2 to 20.2R3 or later fixed guidance.
- Upgrade 20.3 to 20.3R2 or later fixed guidance.
- Review Juniper JSA11158 for current vendor remediation details.
- Confirm whether DHCP relay active-lease query is required on exposed subscriber paths.
Validation and detection
- Inventory Junos OS devices and record exact release trains.
- Check whether devices run Junos OS Evolved; sources state it is unaffected.
- Review configuration for DHCP Relay Agent active-lease query usage.
- Correlate jdhcpd cores or restarts with DHCP traffic anomalies.
- Verify upgraded devices are at or beyond Juniper fixed releases.
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
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ATT&CK lookup starting points
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Open ATT&CK lookupCVE-2021-0267 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 7.4 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
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:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H2.84Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.4HighVector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://kb.juniper.net/JSA11158CVE reference · x_refsource_MISC
- https://www.juniper.net/documentation/us/en/software/junos/subscriber-mgmt-sessions/topics/ref/statement/active-leasequery-edit-forwarding-options.htmlCVE reference · x_refsource_MISC
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.