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JunosOperating system · Juniper

CVE-2021-0223

HIGH · 7.8 CVSS v3.1 Published 2021-01-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
80/100
Remediation priority · High
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 local privilege escalation vulnerability in telnetd.real of Juniper Networks Junos OS may allow a locally authenticated shell user to escalate privileges and execute arbitrary commands as root. telnetd.real is shipped with setuid permissions enabled and is owned by the root user, allowing local users to run telnetd.real with root privileges. This issue affects Juniper Networks Junos OS: all versions prior to 15.1R7-S9; 17.3 versions prior to 17.3R3-S11; 17.4 versions prior to 17.4R2-S12, 17.4R3-S3; 18.1 versions prior to 18.1R3-S11; 18.2 versions prior to 18.2R3-S6; 18.3 versions prior to 18.3R2-S4, 18.3R3-S4; 18.4 versions prior to 18.4R2-S7, 18.4R3-S6; 19.1 versions prior to 19.1R2-S2, 19.1R3-S4; 19.2 versions prior to 19.2R1-S6, 19.2R3-S1; 19.3 versions prior to 19.3R3-S1; 19.4 versions prior to 19.4R2-S2, 19.4R3; 20.1 versions prior to 20.1R1-S4, 20.1R2; 20.2 versions prior to 20.2R2.

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 local privilege escalation vulnerability exists in telnetd.real of Juniper Networks Junos OS. The telnet daemon binary is shipped with setuid root permissions and owned by root, allowing any locally authenticated shell user to execute it and gain root-level privileges.

MitigationRemove setuid permissions from telnetd.real or upgrade to a Junos OS version that addresses this vulnerability (15.1R7-S9, 17.3R3-S11, 17.4R2-S12, 18.1R3-S11, 18.2R3-S6, 18.3R2-S4, 18.4R2-S7, 19.1R3-S4, 19.2R3-S1, 19.3R3-S1, 19.4R3, 20.1R2, or 20.2R2 or later).

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:= 15.1= 17.3= 17.4= 18.1= 18.2= 18.3= 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
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/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. Locate the telnetd.real binary
    Use the 'find' command to locate any file named telnetd.real on the system: find / -name telnetd.real 2>/dev/null
    Affected if The telnetd.real binary exists on the system
  2. Check setuid permissions on telnetd.real
    Run 'ls -la' on the located telnetd.real binary and look for 's' in the owner permissions (e.g., -rwsr-xr-x). The setuid bit is indicated by an 's' in the owner's execute position.
    Affected if The binary has the setuid bit set (shown as -rwsr-xr-x or similar with 's' in owner execute)
  3. Verify root ownership
    Run 'ls -la' on the telnetd.real binary and confirm the owner is listed as 'root'
    Affected if The binary is owned by root
  4. Confirm Junos OS version
    Run 'show version' or check /etc/*release* to obtain the installed Junos OS version number
    Affected if The installed version matches or falls within the affected ranges: 15.1, 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, or 20.1

A user is affected if the telnetd.real binary exists with setuid root permissions AND the Junos OS version matches one of the listed affected versions, allowing any local shell user to escalate to root privileges.

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

Remove setuid permissions from telnetd.real or upgrade to a Junos OS version that addresses this vulnerability (15.1R7-S9, 17.3R3-S11, 17.4R2-S12, 18.1R3-S11, 18.2R3-S6, 18.3R2-S4, 18.4R2-S7, 19.1R3-S4, 19.2R3-S1, 19.3R3-S1, 19.4R3, 20.1R2, or 20.2R2 or later).

Fix this in Junos Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,440
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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-2021-0223 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
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