iOSOperating system · Cisco
CVE-2020-3477
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 vulnerability in the CLI parser of Cisco IOS Software and Cisco IOS XE Software could allow an authenticated, local attacker to access files from the flash: filesystem. The vulnerability is due to insufficient application of restrictions during the execution of a specific command. An attacker could exploit this vulnerability by using a specific command at the command line. A successful exploit could allow the attacker to obtain read-only access to files that are located on the flash: filesystem that otherwise might not have been accessible.
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 vulnerability in the CLI parser of Cisco IOS and IOS XE Software allows an authenticated local attacker to read files from the flash: filesystem by exploiting insufficient access restrictions during execution of a specific command. The attacker needs valid credentials to access the command line, but can then access files that should otherwise be restricted.
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
iOSOperating system
= 16.3.11CVSS 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
- None
- Availability
- None
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
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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Determine Cisco iOS versionConnect to the device CLI and execute the 'show version' command. Locate the version number in the output (typically displayed as 'Version 16.3.11' or similar).Affected if The displayed iOS version is exactly 16.3.11
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Verify CLI access existsConfirm that local CLI authentication is configured on the device. Check for local user accounts or enable password configuration using 'show running-config | include username|enable'Affected if Local user accounts or enable credentials are configured, providing authenticated CLI access
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Check flash: filesystem accessibilityFrom the CLI, attempt to access the flash: filesystem using directory commands such as 'dir flash:' to confirm the filesystem is accessible to authenticated users.Affected if The flash: directory contents are visible to authenticated CLI users (non-privileged or privileged)
The device is affected if it runs exactly Cisco iOS version 16.3.11 and an authenticated user can access the CLI to read files from the flash: filesystem.
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 relevant Cisco IOS/IOS XE software update (refer to Cisco advisory) to patch the CLI parser vulnerability. Restrict physical and console access to trusted personnel only.
Fix this in iOS
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,120.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-3477 — 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-2020-3477 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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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.
- 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
- No spam, self-promotion, credentials, or personal data