Security readout for executives and security teams
Plain-English summary
This is a network-facing denial-of-service issue in Juniper Junos OS on ACX500 and ACX4000 routers. A remote attacker could disrupt forwarding by sending a high rate of specific packets, causing the Forwarding Engine Board to crash. Continued traffic can keep the outage going.
Executive priority
Treat as high priority where affected ACX routers support customer, edge, or critical network paths. The issue is availability-only, but the business impact can be significant if routing disruption affects services or revenue operations.
Technical view
CVE-2021-0233 affects Junos OS 17.4 versions before 17.4R3-S2 on ACX500 and ACX4000 Series. The CVSS 3.1 vector is AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, reflecting unauthenticated remote availability impact without confidentiality or integrity loss.
Likely exposure
Exposure is limited to Juniper ACX500 and ACX4000 devices running Junos OS 17.4 earlier than 17.4R3-S2. Internet-facing or untrusted-network-facing routing infrastructure has higher business impact because successful denial of service can affect network availability.
Exploitation context
The supplied sources do not show CISA KEV listing or active exploitation. The described attack condition is remote and unauthenticated, but requires a high rate of specific packets. Continued receipt sustains the denial-of-service state.
Researcher notes
The source bundle names only ACX500 Series, ACX4000 Series, and Junos OS 17.4 prior to 17.4R3-S2. It does not provide packet details, exploit indicators, workarounds, or evidence of exploitation; avoid expanding scope beyond those products and versions.
Mitigation direction
- Inventory ACX500 and ACX4000 devices running Junos OS 17.4.
- Move affected devices off versions earlier than 17.4R3-S2 per Juniper guidance.
- Review Juniper advisory JSA11128 for the supported fixed target release.
- Prioritize exposed edge or provider-facing routers before internal-only devices.
Validation and detection
- Confirm model family and Junos OS release for each ACX500 or ACX4000 device.
- Flag Junos OS 17.4 builds earlier than 17.4R3-S2 as vulnerable.
- Review operational logs for Forwarding Engine Board crashes or unexplained forwarding outages.
- Check monitoring for packet-rate spikes correlated with router instability.
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 lookupCWE-794: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-0233 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 7.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://kb.juniper.net/JSA11128CVE 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.