Security readout for executives and security teams
Plain-English summary
Malformed DHCPv6 traffic can crash the Junos OS DHCP daemon on devices configured as a DHCPv6 server or relay. It restarts automatically, but repeated malformed traffic can keep DHCPv6 disrupted. This is availability-only, with possible impact to IPv6 address assignment or relay services.
Executive priority
Treat this as a high-priority availability issue for IPv6-dependent networks. It is not a data theft vulnerability, but repeated daemon crashes can disrupt DHCPv6 service on affected Juniper infrastructure.
Technical view
CVE-2021-0240 affects Junos OS 17.3 through 20.4 before specified fixed releases when JDHCPD handles DHCPv6 as local server or relay agent. A malformed DHCPv6 packet can trigger a JDHCPD crash and restart. Continued packets can sustain DoS. DHCPv4 is not affected. CVSS 3.1 score is 7.4.
Likely exposure
Exposure is limited to Juniper Junos OS systems running affected versions and configured for DHCPv6 local server or DHCPv6 relay. The CVSS vector indicates adjacent-network reachability, no privileges, and no user interaction.
Exploitation context
The supplied sources do not cite public exploitation or CISA KEV listing. The risk is practical denial of service if an adjacent attacker can repeatedly deliver malformed DHCPv6 packets to an affected configuration.
Researcher notes
Key constraints are configuration and protocol scope: affected Junos OS versions must run DHCPv6 server or relay, and DHCPv4 is unaffected. Evidence provided names fixed version thresholds but does not provide exploit details or independent exploitation confirmation.
Mitigation direction
- Upgrade Junos OS to the fixed release for the deployed version branch.
- Prioritize devices providing DHCPv6 local server or relay services.
- Confirm DHCPv4-only deployments are not misclassified as affected.
- Review Juniper JSA11168 for branch-specific remediation guidance.
- Monitor for repeated JDHCPD crashes until remediation is complete.
Validation and detection
- Inventory Junos OS versions across Juniper platforms.
- Identify devices configured as DHCPv6 local server or relay agent.
- Compare each version against Juniper’s fixed-release list.
- Check operational logs for recurring JDHCPD crash or restart events.
- After upgrade, verify DHCPv6 service continuity in regression testing.
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
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ATT&CK lookup starting points
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Open ATT&CK lookupCVE-2021-0240 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/JSA11168CVE 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.
Improper Check or Handling of Exceptional Conditions
Improper Check or Handling of Exceptional Conditions represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.