Security readout for executives and security teams
Plain-English summary
Certain older Juniper EX switches can be knocked offline by someone on the same local network segment sending crafted ARP traffic. The impact is availability only, but repeated traffic can keep the outage going. This is most urgent where affected switches support critical office, data center, or operational networks.
Executive priority
Treat as a moderate availability risk. Prioritize remediation for affected switches in critical network paths or shared Layer 2 environments where an adjacent attacker or compromised host could cause operational disruption.
Technical view
CVE-2021-0271 is a CWE-415 double-free flaw in the Junos OS software forwarding interface daemon, sfid. On listed Marvell-chipset EX Series platforms, processing a crafted ARP packet from an adjacent attacker can crash sfid and cause denial of service. Affected releases are Junos OS 12.3 before 12.3R12-S17 and 15.1 before 15.1R7-S8.
Likely exposure
Exposure is limited to the named Juniper EX Series models running affected Junos OS 12.3 or 15.1 releases. The attacker must be adjacent on the network, so internet-wide exposure is not indicated by the supplied sources.
Exploitation context
The source bundle does not report active exploitation, and KEV status is false. The attack requires local network adjacency and crafted ARP processing. Repeated malicious traffic can sustain the denial-of-service condition, but the supplied evidence does not indicate confidentiality or integrity impact.
Researcher notes
The key boundary is adjacency: this is not described as remotely exploitable over the internet. The affected scope is explicitly limited to listed Marvell-chipset EX Series devices. Do not generalize to other Juniper products without vendor evidence.
Mitigation direction
- Upgrade affected Junos OS 12.3 systems to 12.3R12-S17 or later.
- Upgrade affected Junos OS 15.1 systems to 15.1R7-S8 or later.
- Confirm Juniper guidance for platform-specific upgrade paths and support constraints.
- Reduce untrusted Layer 2 adjacency to affected EX switches where feasible.
- Monitor for sfid crashes, core files, or unexplained switch availability events.
Validation and detection
- Inventory EX2200-C, EX3200, EX3300, EX4200, EX4500, EX4550, EX6210, EX8208, and EX8216 devices.
- Check whether each listed device runs Junos OS 12.3 before 12.3R12-S17 or 15.1 before 15.1R7-S8.
- Confirm whether each device is a listed Marvell-chipset based EX Series platform.
- Review device logs and core files for sfid process crashes.
- Verify upgrade completion against Juniper advisory 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
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
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CWE-415: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-0271 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
- Medium
- CVSS
- 6.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:A/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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H2.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.5MediumVector: CVSS:3.1/AV:A/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/JSA11162CVE 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.
Double Free
Double Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.