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JunosOperating system · Juniper

CVE-2020-1661

MEDIUM · 5.3 CVSS v3.1 Published 2020-10-16
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable 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
On Juniper Networks Junos OS devices configured as a DHCP forwarder, the Juniper Networks Dynamic Host Configuration Protocol Daemon (jdhcp) process might crash when receiving a malformed DHCP packet. This issue only affects devices configured as DHCP forwarder with forward-only option, that forward specified DHCP client packets, without creating a new subscriber session. The jdhcpd daemon automatically restarts without intervention, but continuous receipt of the malformed DHCP packet will repeatedly crash jdhcpd, leading to an extended Denial of Service (DoS) condition. This issue can be triggered only by DHCPv4, it cannot be triggered by DHCPv6. This issue affects Juniper Networks Junos OS: 12.3 versions prior to 12.3R12-S16; 12.3X48 versions prior to 12.3X48-D105 on SRX Series; 14.1X53 versions prior to 14.1X53-D60 on EX and QFX Series; 15.1 versions prior to 15.1R7-S7; 15.1X49 versions prior to 15.1X49-D221, 15.1X49-D230 on SRX Series; 15.1X53 versions prior to 15.1X53-D593 on EX2300/EX3400; 16.1 versions prior to 16.1R7-S5.

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

On Juniper Networks Junos OS devices configured as a DHCP forwarder with the forward-only option, the jdhcpd daemon crashes when processing a malformed DHCPv4 packet. While the daemon auto-restarts, continuous malformed packets cause repeated crashes resulting in sustained denial of service. This issue only affects DHCPv4 traffic and only devices with specific forwarder configurations.

MitigationUpgrade to the fixed Junos OS versions specified in the advisory (12.3R12-S16, 12.3X48-D105, 14.1X53-D60, 15.1R7-S7, 15.1X49-D230, 15.1X53-D593, 16.1R7-S5 or later). If upgrading is not immediately possible, consider disabling the forward-only option or implementing ACL filtering for malformed DHCP packets at network perimeter.

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= 16.1= 12.3x48= 15.1x49= 15.1x53= 14.1x53

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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

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

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. Check Junos OS version
    Run 'show version' command on the device and note the exact Junos version installed
    Affected if Version matches any of these: 12.3, 15.1, 16.1, 12.3X48, 15.1X49, 15.1X53, 14.1X53 (or any minor release within these branches)
  2. Verify DHCP forwarder configuration
    Run 'show configuration forwarding-options helpers bootp' or 'show configuration forwarding-options dhcp-relay' to see if DHCP relay/forwarder is configured
    Affected if DHCP forwarder or relay is configured on the device
  3. Confirm forward-only option is enabled
    Examine the DHCP forwarder configuration output for the 'forward-only' option under the helpers or dhcp-relay hierarchy
    Affected if The 'forward-only' option is explicitly configured within the DHCP forwarder settings
  4. Verify DHCPv4 traffic presence
    Run 'show dhcp relay statistics' or monitor interface traffic for DHCPv4 packets being processed by the forwarder
    Affected if Device is actively processing DHCPv4 traffic through the forwarder

Device is affected if it runs a listed Junos version AND has DHCP forwarder configured with the forward-only option AND is handling DHCPv4 traffic.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to the fixed Junos OS versions specified in the advisory (12.3R12-S16, 12.3X48-D105, 14.1X53-D60, 15.1R7-S7, 15.1X49-D230, 15.1X53-D593, 16.1R7-S5 or later). If upgrading is not immediately possible, consider disabling the forward-only option or implementing ACL filtering for malformed DHCP packets at network perimeter.

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA3.0 h
21.0 hours of engineering $3,680
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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-2020-1661 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
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