CVE-2021-31360
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 · uneditedAn improper privilege management vulnerability in the Juniper Networks Junos OS and Junos OS Evolved command-line interpreter (CLI) allows a low-privileged user to overwrite local files as root, possibly leading to a system integrity issue or Denial of Service (DoS). Depending on the files overwritten, exploitation of this vulnerability could lead to a sustained Denial of Service (DoS) condition, requiring manual user intervention to recover. Systems are only vulnerable if jdhcpd is running, which can be confirmed via the 'show system processes' command. For example: root@host# run show system processes extensive | match dhcp 26537 root -16 0 97568K 13692K RUN 0 0:01 3.71% jdhcpd This issue affects: Juniper Networks Junos OS: All versions, including the following supported releases: 15.1 versions prior to 15.1R7-S10; 17.4 versions prior to 17.4R3-S5; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S9; 19.1 versions prior to 19.1R3-S6; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S3; 19.4 versions prior to 19.4R3-S6; 20.1 versions prior to 20.1R2-S2, 20.1R3-S1; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R2-S1, 20.4R3; 21.1 versions prior to 21.1R1-S1, 21.1R2. Juniper Networks Junos OS Evolved: All versions prior to 20.4R2-S3-EVO; All versions of 21.1-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 confidenceImproper privilege management vulnerability in Juniper Networks Junos OS and Junos OS Evolved CLI allows authenticated low-privileged users to overwrite local files as root through the jdhcpd daemon, leading to system integrity compromise or sustained Denial of Service.
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= 15.1= 17.4= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1= 20.2= 20.3= 20.4<= 20.3= 20.4= 21.1CVSS 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
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/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 checksWork through these to decide whether this CVE applies to you.
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Identify product and versionRun 'show version' on the device CLI to determine if you are running Junos OS or Junos OS Evolved and note the exact version numberAffected if The device runs Junos OS version 15.1, 17.4, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, 20.3, or 20.4, or Junos OS Evolved version 20.3 or earlier, 20.4, or 21.1
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Verify jdhcpd process is runningExecute 'show system processes extensive | match dhcp' to check if the jdhcpd daemon is active on the systemAffected if The jdhcpd process is listed as running - this daemon must be active for the vulnerability to be exploitable
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Confirm low-privileged user access existsReview user accounts with 'show system users' and check for non-root authenticated users with limited privilegesAffected if There are authenticated low-privileged users configured on the system who can access the CLI
The system is affected if it runs a vulnerable Junos OS/Evolved version AND has jdhcpd running AND has low-privileged authenticated users who could exploit the privilege management flaw in the jdhcpd daemon.
Generated from the published advisory. Verify against your own configuration.
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 · scopedVerify if jdhcpd is running via 'show system processes extensive | match dhcp' and apply vendor-supplied patches for affected Junos OS/Evolved versions; if jdhcpd is not running, the system is not vulnerable.
Junos OS: upgrade to 15.1R7-S10 / 17.4R3-S5 / 18.3R3-S5 / 18.4R3-S9 / 19.1R3-S6 / 19.2R3-S3 / 19.3R3-S3 / 19.4R3-S6 / 20.1R3-S1 / 20.2R3-S2 / 20.3R3 / 20.4R3 / 21.1R2 (or later); Junos OS Evolved: upgrade to 20.4R2-S3-EVO or later
- 1. Identify if the system is running jdhcpd by executing 'run show system processes extensive | match dhcp' at the CLI prompt
- 2. If jdhcpd is running, verify the current Junos OS or Junos OS Evolved version using 'show version'
- 3. For Junos OS: Upgrade to one of the fixed releases: 15.1R7-S10, 17.4R3-S5, 18.3R3-S5, 18.4R3-S9, 19.1R3-S6, 19.2R1-S7, 19.2R3-S3, 19.3R2-S6, 19.3R3-S3, 19.4R3-S6, 20.1R2-S2, 20.1R3-S1, 20.2R3-S2, 20.3R3, 20.4R2-S1, 20.4R3, 21.1R1-S1, or 21.1R2
- 4. For Junos OS Evolved: Upgrade to 20.4R2-S3-EVO or later (or a later stable release)
- 5. After upgrade, verify the jdhcpd process is still functioning correctly and confirm the fix by ensuring the vulnerability is no longer exploitable
- 6. As a temporary mitigation, if jdhcpd is not required, consider disabling it via configuration (deactivate system services dhcp), though this may impact DHCP relay functionality
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-31360 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-31360 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
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