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JunosOperating system · Juniper

CVE-2025-21591

HIGH · 7.4 CVSS v3.1 Published 2025-04-09
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
79/100
Remediation priority · High
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
A Buffer Access with Incorrect Length Value vulnerability in the jdhcpd daemon of Juniper Networks Junos OS, when DHCP snooping is enabled, allows an unauthenticated, adjacent, attacker to send a DHCP packet with a malformed DHCP option to cause jdhcp to crash creating a Denial of Service (DoS) condition. Continuous receipt of these DHCP packets using the malformed DHCP Option will create a sustained Denial of Service (DoS) condition. This issue affects Junos OS: * from 23.1 before 23.2R2-S3, * from 23.4 before 23.4R2-S3, * from 24.2 before 24.2R2. This issue isn't applicable to any versions of Junos OS before 23.1R1. This issue doesn't affect vSRX Series which doesn't support DHCP Snooping. This issue doesn't affect Junos OS Evolved. There are no indicators of compromise for this issue.

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

The jdhcpd daemon in Juniper Junos OS contains a buffer access vulnerability with incorrect length value when processing DHCP packets. When DHCP snooping is enabled, an adjacent unauthenticated attacker can send DHCP packets with malformed DHCP options, causing the jdhcpd daemon to crash and create a denial of service. Continuous receipt of these malformed packets sustains the DoS condition.

MitigationUpgrade to Junos OS version 23.2R2-S3, 23.4R2-S3, or 24.2R2 as appropriate for the deployed branch, or temporarily disable DHCP snooping if upgrade cannot be performed immediately.

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:= 23.1= 23.2= 23.4= 24.2

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
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/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' or 'show system information' to display the installed Junos OS version
    Affected if Version listed is 23.1, 23.2, 23.4, or 24.2 (exact match to affected releases)
  2. Verify DHCP snooping configuration
    Run 'show dhcp snooping' or 'show configuration | display set | match dhcp-snooping' to check if DHCP snooping is enabled
    Affected if DHCP snooping is enabled (this is required for the vulnerability to be exploitable)
  3. Check jdhcpd daemon status
    Run 'show system processes extensive | match jdhcpd' or check daemon health via 'request system process dump jdhcpd' if available
    Affected if jdhcpd daemon is not running or has recently restarted unexpectedly
  4. Review system logs for jdhcpd crashes
    Run 'show log messages | match jdhcpd' or 'show system core-dumps' to look for evidence of jdhcpd daemon crashes
    Affected if Recent jdhcpd crash events appear in logs with DHCP-related error details

Affected if running Junos OS version 23.1, 23.2, 23.4, or 24.2 AND DHCP snooping is currently enabled on the device.

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

Upgrade to Junos OS version 23.2R2-S3, 23.4R2-S3, or 24.2R2 as appropriate for the deployed branch, or temporarily disable DHCP snooping if upgrade cannot be performed immediately.

Recommended fix High confidence

Upgrade to 23.2R2-S3 / 23.4R2-S3 / 24.2R2 (or later) depending on your current branch

  1. 1. Identify the current Junos OS version by running 'show version'
  2. 2. Based on current version, determine the minimum fixed release: if 23.1.x upgrade to 23.2R2-S3 or later; if 23.4.x upgrade to 23.4R2-S3 or later; if 24.2.x upgrade to 24.2R2 or later
  3. 3. Download the appropriate Junos OS upgrade image from the Juniper support portal (supportportal.juniper.net)
  4. 4. Back up the current configuration using 'request system backup' or similar
  5. 5. Upload the upgrade image to the device
  6. 6. Install the upgrade using 'request system software add <image>' and reboot
  7. 7. After reboot, verify the new version is running with 'show version'
  8. 8. Confirm DHCP snooping functionality is operational and the device is not crashing
Caveat Review Juniper upgrade guide for your platform; standard Junos OS upgrade procedures apply - test in lab first if possible

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

Fix this in Junos Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,640
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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-2025-21591 in production — separate from our analysis above.

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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
  • No spam, self-promotion, credentials, or personal data