Security readout for executives and security teams
Plain-English summary
Some Juniper Junos OS Evolved routers can drop established IPv6 BGP sessions after receiving a specific IPv6 packet. Repeated packets can keep routing disrupted, creating a sustained denial-of-service condition. IPv4 BGP sessions and non-Evolved Junos OS releases are not reported affected in the source bundle.
Executive priority
Treat this as high priority for networks where IPv6 BGP carries production routing. The likely business impact is routing instability or outage, not data theft. Remediation urgency depends on whether affected Junos OS Evolved versions and IPv6 BGP peers are present.
Technical view
CVE-2021-0226 affects Junos OS Evolved 19.4, 20.1, 20.2, and 20.3 before specified fixed EVO releases. The issue impacts IPv6 IBGP or EBGP sessions, causing session termination and high availability impact. CVSS 3.1 is 7.1 with adjacent attack vector, no privileges, and no user interaction.
Likely exposure
Exposure is most likely in networks running Junos OS Evolved on affected versions with IPv6 IBGP or EBGP peering enabled. Environments using only IPv4 BGP, or standard Junos OS rather than Junos OS Evolved, are not identified as affected by the provided sources.
Exploitation context
The source bundle does not show CISA KEV listing or cited evidence of active exploitation. The CVSS vector indicates no authentication or user interaction is required, but adjacent-network reachability is part of the scoring. Packet details are not provided, limiting independent exploitability assessment.
Researcher notes
The public bundle confirms affected version ranges, protocol scope, CVSS, and fixed-version thresholds. It does not provide packet structure, proof-of-concept status, operational workarounds, or exploitation telemetry. Avoid assuming impact beyond IPv6 BGP session termination on Junos OS Evolved.
Mitigation direction
- Upgrade Junos OS Evolved to the fixed release for the deployed train.
- Use Juniper advisory JSA11121 as the authoritative remediation source.
- Prioritize routers carrying production IPv6 IBGP or EBGP sessions.
- If upgrade is delayed, check Juniper guidance for supported temporary controls.
- Monitor IPv6 BGP stability until remediation is complete.
Validation and detection
- Inventory devices running Junos OS Evolved and record exact release versions.
- Identify IPv6 IBGP and EBGP sessions on those devices.
- Compare versions against the fixed EVO release thresholds in the advisory.
- Review routing logs for repeated IPv6 BGP session flaps.
- Confirm remediation by verifying upgraded software versions.
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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CWE-665: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-0226 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 7.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/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:U/C:N/I:L/A:H2.84.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.1HighVector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://kb.juniper.net/JSA11121CVE 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 Initialization
Improper Initialization represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.