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Ios Xe Rom MonitorOperating system · Cisco

CVE-2020-3524

MEDIUM · 6.8 CVSS v3.1 Published 2020-09-24
Fix available
A fix is available. Upgrade to 15.6 / 16.2 or later.
See remediation →
73/100
Remediation priority · Elevated
No privileges 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 the Cisco IOS XE ROM Monitor (ROMMON) Software for Cisco 4000 Series Integrated Services Routers, Cisco ASR 920 Series Aggregation Services Routers, Cisco ASR 1000 Series Aggregation Services Routers, and Cisco cBR-8 Converged Broadband Routers could allow an unauthenticated, physical attacker to break the chain of trust and load a compromised software image on an affected device. The vulnerability is due to the presence of a debugging configuration option in the affected software. An attacker could exploit this vulnerability by connecting to an affected device through the console, forcing the device into ROMMON mode, and writing a malicious pattern using that specific option on the device. A successful exploit could allow the attacker to break the chain of trust and load a compromised software image on the affected device. A compromised software image is any software image that has not been digitally signed by Cisco.

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 vulnerability in Cisco IOS XE ROMMON firmware on specified router models (4000 Series ISR, ASR 920, ASR 1000, cBR-8) contains a debugging configuration option that can be exploited by a physical attacker with console access. By forcing the device into ROMMON mode and writing a malicious pattern using this option, an attacker can bypass the secure boot chain of trust and load unsigned firmware.

MitigationRestrict physical access to device console ports and apply Cisco's firmware updates that remove or disable the vulnerable debugging option. Monitor for unauthorized console connections.

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
Ios Xe Rom MonitorOperating system
Affected:< 16.2\(1r\)< 15.6\(18r\)< 16.4\(1r\)s

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

CVSS:3.1/AV:P/AC:L/PR:N/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. Identify the router model
    Use 'show version' command or check physical hardware labeling to determine if the device is a 4000 Series ISR, ASR 920, ASR 1000, or cBR-8 model
    Affected if The device is NOT one of these four models (4000 Series ISR, ASR 920, ASR 1000, cBR-8)
  2. Determine the ROMMON version
    Access ROMMON mode by rebooting the device and pressing Break key, then use the 'version' command to display the ROMMON firmware version
    Affected if The ROMMON version is less than 16.2(1), less than 15.6(18), or less than 16.4(1s)
  3. Check for the debugging configuration option
    In ROMMON mode, look for the 'bypass-secure-boot' or similar debugging configuration option using '?' or 'help' command
    Affected if The debugging option that allows writing arbitrary patterns is present and accessible in ROMMON mode
  4. Verify physical security of console access
    Inspect the device location and console port protections. Use 'show users' command to check for active console sessions
    Affected if Console ports are physically accessible to unauthorized persons or show unexpected active console connections

A device is affected if it is a 4000 Series ISR, ASR 920, ASR 1000, or cBR-8 with ROMMON version below the fixed releases and the device console is accessible to untrusted individuals.

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
Upgrade available Upgrade to 15.6 / 16.2 / 16.4 or later
Fixed in 15.616.216.4
Interim mitigation

Restrict physical access to device console ports and apply Cisco's firmware updates that remove or disable the vulnerable debugging option. Monitor for unauthorized console connections.

Fix this in Ios Xe Rom Monitor Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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Scan for this in your stack

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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-2020-3524 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
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data