CVE-2021-31357
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 · uneditedA command injection vulnerability in tcpdump command processing on Juniper Networks Junos OS Evolved allows an attacker with authenticated CLI access to be able to bypass configured access protections to execute arbitrary shell commands within the context of the current user. The vulnerability allows an attacker to bypass command authorization restrictions assigned to their specific user account and execute commands that are available to the privilege level for which the user is assigned. For example, a user that is in the super-user login class, but restricted to executing specific CLI commands could exploit the vulnerability to execute any other command available to an unrestricted admin user. This vulnerability does not increase the privilege level of the user, but rather bypasses any CLI command restrictions by allowing full access to the shell. This issue affects Juniper Networks Junos OS Evolved: All versions prior to 20.3R2-S1-EVO; 20.4 versions prior to 20.4R2-S2-EVO; 21.1 versions prior to 21.1R2-EVO; 21.2 versions prior to 21.2R1-S1-EVO, 21.2R2-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 confidenceA command injection vulnerability in tcpdump command processing on Juniper Networks Junos OS Evolved allows an authenticated CLI user to bypass configured command authorization restrictions and execute arbitrary shell commands within the context of the current user. The vulnerability does not escalate privileges but allows restricted users to access the full shell, bypassing CLI command restrictions assigned to their account.
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<= 20.3= 20.4= 21.1= 21.2CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Identify Junos OS Evolved versionRun `show version` or `show version detail` from the CLI to obtain the exact software versionAffected if The version is 20.3 or earlier, 20.4, 21.1, or 21.2 (any build within these releases)
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Verify user role and permissionsRun `show system user username <your_user>` to check the assigned class/role for the account in questionAffected if The user is assigned a restricted class (such as operator, read-only, or super-user with limited CLI access) rather than full super-user privileges
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Confirm tcpdump command availabilityRun `which tcpdump` or attempt `tcpdump --help` from the CLI to see if the tcpdump utility is accessible to the current userAffected if tcpdump is executable by the user in question
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Check for unauthorized shell access attemptsReview system logs with `show log messages` or `show system users` for any unexpected shell spawns or privilege escalation eventsAffected if Logs show shell access or command execution that should have been blocked by the user's authorization restrictions
You are affected if your Junos OS Evolved version falls within the affected ranges AND an authenticated user with restricted CLI permissions was able to execute tcpdump or access the shell to bypass command authorization.
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 · scopedApply the vendor-provided patches for Junos OS Evolved: upgrade to 20.3R2-S1-EVO or later, 20.4R2-S2-EVO or later, 21.1R2-EVO or later, or 21.2R1-S1-EVO/21.2R2-EVO or later. Until patched, restrict CLI access to trusted personnel only.
20.3R2-S1-EVO, 20.4R2-S2-EVO, 21.1R2-EVO, 21.2R1-S1-EVO, or 21.2R2-EVO (or later)
- Identify the current Junos OS Evolved version using 'show version' command
- Review the Juniper Networks upgrade guide for Junos OS Evolved at kb.juniper.net
- Schedule a maintenance window for the upgrade
- Back up the current configuration using 'request system configuration rescue save'
- Upgrade to a fixed version: 20.3R2-S1-EVO or later, 20.4R2-S2-EVO or later, 21.1R2-EVO or later, or 21.2R1-S1-EVO/21.2R2-EVO or later
- Verify the upgrade was successful using 'show version'
- Confirm the fixed version is running and the vulnerability is patched
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation4.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-31357 — 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-2021-31357 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
No notes yet
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- Version or environment caveats, and links to real fixes
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