CVE-2021-0206
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 NULL Pointer Dereference vulnerability in Juniper Networks Junos OS allows an attacker to send a specific packet causing the packet forwarding engine (PFE) to crash and restart, resulting in a Denial of Service (DoS). By continuously sending these specific packets, an attacker can repeatedly disable the PFE causing a sustained Denial of Service (DoS). This issue only affects Juniper Networks NFX Series, SRX Series platforms when SSL Proxy is configured. This issue affects Juniper Networks Junos OS on NFX Series and SRX Series: 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R3-S1; 19.1 versions prior to 19.1R1-S6, 19.1R2-S2, 19.1R3; 19.2 versions prior to 19.2R1-S2, 19.2R2; 19.3 versions prior to 19.3R2. This issue does not affect Juniper Networks Junos OS versions on NFX Series and SRX Series prior to 18.3R1.
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 NULL pointer dereference vulnerability in Juniper Junos OS allows remote attackers to crash the Packet Forwarding Engine (PFE) by sending specially crafted packets to devices with SSL Proxy configured on NFX Series and SRX Series platforms, causing a denial of service that can be repeatedly exploited.
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= 18.3= 18.4= 19.1= 19.2= 19.3CVSS 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
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/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 checksWork through these to decide whether this CVE applies to you.
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Identify the Junos OS versionRun 'show version' or 'system rollback' command to confirm the installed Junos OS versionAffected if The version matches 18.3, 18.4, 19.1, 19.2, or 19.3 (any variant within these branches)
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Confirm the hardware platformRun 'show chassis hardware' or check the device model to verify it is an NFX Series or SRX Series deviceAffected if The device is an NFX or SRX Series platform
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Check if SSL Proxy is configuredRun 'show services ssl proxy configuration' or examine the configuration under 'set services ssl proxy' hierarchyAffected if SSL Proxy is enabled or configured on the device
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Verify SSL Proxy is actively bound to an interfaceRun 'show services ssl proxy statistics' to see if SSL Proxy is actively processing traffic on any interfaceAffected if SSL Proxy is bound and actively processing traffic
A device is affected if it runs Junos OS version 18.3, 18.4, 19.1, 19.2, or 19.3 on NFX or SRX Series hardware AND has SSL Proxy configured and active.
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.
From vendor dataApply the vendor-supplied Junos OS patches for versions 18.3, 18.4, 19.1, 19.2, and 19.3 as specified in the advisory. If patching is not immediately feasible, consider disabling SSL Proxy if operationally acceptable or implementing network-based filtering to limit exposure.
- 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-2021-0206 — 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-2021-0206 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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- 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
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