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JunosOperating system · Juniper

CVE-2021-0277

HIGH · 8.8 CVSS v3.1 Published 2021-07-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
93/100
Remediation priority · Urgent
No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
An Out-of-bounds Read vulnerability in the processing of specially crafted LLDP frames by the Layer 2 Control Protocol Daemon (l2cpd) of Juniper Networks Junos OS and Junos OS Evolved may allow an attacker to cause a Denial of Service (DoS), or may lead to remote code execution (RCE). Continued receipt and processing of these frames, sent from the local broadcast domain, will repeatedly crash the l2cpd process and sustain the Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS: 12.3 versions prior to 12.3R12-S18; 15.1 versions prior to 15.1R7-S9; 17.3 versions prior to 17.3R3-S12; 17.4 versions prior to 17.4R2-S13, 17.4R3-S5; 18.1 versions prior to 18.1R3-S13; 18.2 versions prior to 18.2R3-S8; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R2-S8, 18.4R3-S8; 19.1 versions prior to 19.1R3-S5; 19.2 versions prior to 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R1-S4, 19.4R2-S4, 19.4R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3; 20.2 versions prior to 20.2R3-S1; 20.3 versions prior to 20.3R2-S1, 20.3R3; 20.4 versions prior to 20.4R2. Juniper Networks Junos OS Evolved versions prior to 20.4R2-EVO.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

An out-of-bounds read vulnerability exists in the Layer 2 Control Protocol Daemon (l2cpd) when processing specially crafted LLDP frames in Juniper Networks Junos OS and Junos OS Evolved. Attackers on the local broadcast domain can send malicious LLDP frames that cause l2cpd to read beyond allocated memory boundaries, leading to repeated daemon crashes and sustained DoS, with potential for remote code execution.

MitigationApply the vendor-supplied Junos OS patches to all affected versions (12.3R12-S18, 15.1R7-S9, 17.3R3-S12, 17.4R2-S13, 18.1R3-S13, 18.2R3-S8, 18.3R3-S5, 18.4R2-S8, 19.1R3-S5, 19.2R3-S3, 19.3R2-S6, 19.4R1-S4, 20.1R2-S2, 20.2R3-S1, 20.3R2-S1, or 20.4R2 and later). As a compensating control, consider disabling LLDP on untrusted interfaces if not required.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
JunosOperating system
Affected:= 12.3= 15.1= 17.3= 17.4= 18.1= 18.2= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Junos OS version
    Run `show version` on the device CLI to obtain the installed Junos OS version
    Affected if The version matches any of the affected ranges: 12.3, 15.1, 17.3, 17.4, 18.1, 18.2, 18.4, 19.1, 19.2, 19.3, 19.4, or 20.1 (including their sub-versions)
  2. Verify l2cpd daemon is running
    Run `show system processes daemon | match l2cpd` or check process list via `ps aux | grep l2cpd` to confirm the Layer 2 Control Protocol Daemon is active
    Affected if The l2cpd process is running on the device (required for exploitation)
  3. Check if LLDP is enabled on any interface
    Run `show lldp interface` or `show lldp neighbors` to list interfaces with LLDP enabled
    Affected if LLDP is enabled on one or more interfaces (the vulnerability is triggered by malicious LLDP frames)
  4. Confirm LLDP operational status
    Run `show lldp` to see overall LLDP status and whether it is globally enabled or enabled on specific ports
    Affected if LLDP is globally enabled or enabled on accessible ports (attackers must be on the local broadcast domain to send malicious frames)

Environment is affected only if running a vulnerable Junos version (12.3 through 20.1) AND the l2cpd daemon is active AND LLDP is enabled on accessible interfaces, allowing attackers on the local broadcast domain to send malicious LLDP frames.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the vendor-supplied Junos OS patches to all affected versions (12.3R12-S18, 15.1R7-S9, 17.3R3-S12, 17.4R2-S13, 18.1R3-S13, 18.2R3-S8, 18.3R3-S5, 18.4R2-S8, 19.1R3-S5, 19.2R3-S3, 19.3R2-S6, 19.4R1-S4, 20.1R2-S2, 20.2R3-S1, 20.3R2-S1, or 20.4R2 and later). As a compensating control, consider disabling LLDP on untrusted interfaces if not required.

Recommended fix High confidence

Upgrade to 20.4R2 or later for Junos OS (or 20.4R2-EVO for Junos OS Evolved). For older branches, upgrade to the specific fixed release: 12.3R12-S18, 15.1R7-S9, 17.3R3-S12, 17.4R2-S13 or 17.4R3-S5, 18.1R3-S13, 18.2R3-S8, 18.3R3-S5, 18.4R2-S8 or 18.4R3-S8, 19.1R3-S5, 19.2R3-S3, 19.3R2-S6 or 19.3R3-S2

  1. 1. Identify the current Junos OS version running on the device using 'show version'
  2. 2. Determine which upgrade path applies based on the current version branch (12.3, 15.1, 17.3, 17.4, etc.)
  3. 3. Download the appropriate fixed release from the Juniper Networks support portal
  4. 4. Upload the Junos OS upgrade package to the device via FTP/SCP
  5. 5. Install the upgrade using 'request system software add <package-name>' command
  6. 6. Reboot the device using 'request system reboot' command to complete the installation
  7. 7. After reboot, verify the new version is running with 'show version' and confirm the l2cpd process stability
Caveat Standard Junos upgrade considerations apply - review Juniper release notes for any compatibility alerts or configuration changes required between major versions

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Junos Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing6.0 h
  • Review / QA3.0 h
27.0 hours of engineering $4,800
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-0277 in production — separate from our analysis above.

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