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JunosOperating system · Juniper

CVE-2021-0293

MEDIUM · 5.5 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 →
57/100
Remediation priority · Elevated
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 vulnerability in Juniper Networks Junos OS caused by Missing Release of Memory after Effective Lifetime leads to a memory leak each time the CLI command 'show system connections extensive' is executed. The amount of memory leaked on each execution depends on the number of TCP connections from and to the system. Repeated execution will cause more memory to leak and eventually daemons that need to allocate additionally memory and ultimately the kernel to crash, which will result in traffic loss. Continued execution of this command will cause a sustained Denial of Service (DoS) condition. An administrator can use the following CLI command to monitor for increase in memory consumption of the netstat process, if it exists: user@junos> show system processes extensive | match "username|netstat" PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU COMMAND 21181 root 100 0 5458M 4913M CPU3 2 0:59 97.27% netstat The following log message might be observed if this issue happens: kernel: %KERN-3: pid 21181 (netstat), uid 0, was killed: out of swap space This issue affects Juniper Networks Junos OS 18.2 versions prior to 18.2R2-S8, 18.2R3-S7. 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R1-S8, 18.4R2-S6, 18.4R3-S7; 19.1 versions prior to 19.1R1-S6, 19.1R2-S2, 19.1R3-S4; 19.2 versions prior to 19.2R1-S6, 19.2R3-S2; 19.3 versions prior to 19.3R2-S6, 19.3R3-S1; 19.4 versions prior to 19.4R1-S4, 19.4R2-S3, 19.4R3-S1; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R2-S1, 20.2R3; 20.3 versions prior to 20.3R1-S1, 20.3R2; This issue does not affect Juniper Networks Junos OS versions prior to 18.2R1.

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

A memory leak vulnerability in Juniper Networks Junos OS results from missing release of memory after effective lifetime when the CLI command 'show system connections extensive' is executed. Each execution leaks memory proportional to the number of TCP connections, and repeated execution exhausts memory leading to daemon crashes, kernel panic, traffic loss, and sustained DoS.

MitigationUpgrade Junos OS to the fixed versions specified in the advisory (18.2R2-S8 or later for 18.2 branch, 18.3R3-S4 or later for 18.3 branch, etc.). Monitor netstat process memory consumption as shown in the advisory as a compensating control until patching is possible.

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:= 18.2= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1= 20.2= 20.3

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
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/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. Check Junos OS version
    Execute 'show version' via CLI and locate the Junos version string (e.g., 18.2R1, 19.3R3, etc.)
    Affected if The version matches any of these: 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, or 20.3 (exact version match per advisory)
  2. Identify execution of vulnerable command
    Review system logs or command history for instances of 'show system connections extensive' being executed
    Affected if The command 'show system connections extensive' has been run on the device
  3. Monitor netstat daemon memory usage
    Execute 'show system processes memory' or 'show system connections extensive' while observing the netstat daemon memory consumption via 'show system processes extensive' | match netstat
    Affected if Memory usage of the netstat process continuously grows without being freed after command execution
  4. Check for daemon crash or instability events
    Review system logs (via 'show log messages') for daemon restart events, kernel panic indicators, or unexpected service interruptions
    Affected if The netstat daemon or other Junos daemons have crashed or restarted unexpectedly, especially following execution of the vulnerable command

The device is affected if it runs a Junos version in the 18.2-20.3 range AND the 'show system connections extensive' command has been executed, causing observable memory growth in the netstat process or daemon instability.

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 Junos OS to the fixed versions specified in the advisory (18.2R2-S8 or later for 18.2 branch, 18.3R3-S4 or later for 18.3 branch, etc.). Monitor netstat process memory consumption as shown in the advisory as a compensating control until patching is possible.

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,840
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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-2021-0293 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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