dbcve.org
Ios XeOperating system · Cisco

CVE-2021-1623

HIGH · 7.7 CVSS v3.1 Published 2021-09-23
Fix available
A fix is available. Upgrade to 17.6.1a or later.
See remediation →
83/100
Remediation priority · High
Remotely reachable 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 Simple Network Management Protocol (SNMP) punt handling function of Cisco cBR-8 Converged Broadband Routers could allow an authenticated, remote attacker to overload a device punt path, resulting in a denial of service (DoS) condition. This vulnerability is due to the punt path being overwhelmed by large quantities of SNMP requests. An attacker could exploit this vulnerability by sending a large number of SNMP requests to an affected device. A successful exploit could allow the attacker to overload the device punt path, resulting in a DoS condition.

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 the SNMP punt handling function of Cisco cBR-8 Converged Broadband Routers allows an authenticated, remote attacker to overload the device punt path by sending large quantities of SNMP requests, resulting in denial of service. The punt path handles traffic requiring CPU processing, and when overwhelmed by excessive SNMP requests, it cannot process legitimate traffic, causing device failure.

MitigationImplement SNMP access control lists to restrict which hosts can send SNMP requests, and apply rate limiting on SNMP traffic at network boundaries. Apply Cisco-provided patches or firmware updates when available.

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 XeOperating system
Affected:< 17.6.1a

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
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/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 checks

Work through these to decide whether this CVE applies to you.

  1. Confirm device model is Cisco cBR-8
    Run 'show version' or 'show platform' and look for 'cBR-8' or 'Converged Broadband Router' in the hardware identification output
    Affected if Device is a Cisco cBR-8 Converged Broadband Router
  2. Check IOS XE version
    Run 'show version' and locate the 'IOS XE' or 'software' version line. Compare it to 17.6.1a
    Affected if IOS XE version is lower than 17.6.1a (for example, 17.5.x, 17.4.x, etc.)
  3. Verify SNMP is enabled
    Run 'show snmp' or 'show running-config | include snmp' to check for SNMP configuration. Look for 'snmp-server' commands in the configuration
    Affected if SNMP is configured and enabled on the device
  4. Check SNMP access control configuration
    Run 'show snmp community' or 'show running-config | include snmp-server community' to see which SNMP communities or users are defined and which hosts are permitted
    Affected if SNMP communities or users exist without restrictive ACLs, or SNMP is accessible from untrusted network segments

You are affected if the device is a Cisco cBR-8 running IOS XE version lower than 17.6.1a and SNMP is enabled with accessible community strings.

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.

dbcve · scoped
Upgrade available Upgrade to 17.6.1a or later
Fixed in 17.6.1a
Interim mitigation

Implement SNMP access control lists to restrict which hosts can send SNMP requests, and apply rate limiting on SNMP traffic at network boundaries. Apply Cisco-provided patches or firmware updates when available.

Recommended fix High confidence

Cisco IOS-XE 17.6.1a or later

  1. 1. Verify the current Cisco IOS-XE version on the affected cBR-8 device using 'show version' command
  2. 2. Download Cisco IOS-XE 17.6.1a or later from Cisco's software download center (tools.cisco.com)
  3. 3. Review Cisco release notes for 17.6.1a to ensure compatibility with your specific hardware configuration and other installed features
  4. 4. Create a backup of the current device configuration using 'copy running-config startup-config' or export to external storage
  5. 5. Schedule a maintenance window as the upgrade will require a device reload
  6. 6. Upload the new IOS-XE image to the device's flash storage
  7. 7. Configure the new boot variable: 'boot system flash:<new-image-name>'
  8. 8. Save configuration changes
Caveat Standard Cisco IOS-XE upgrade considerations apply - review release notes for any configuration changes, feature compatibility, or migration requirements specific to 17.6.x train

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Ios Xe Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,640
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,224.

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-2021-1623 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