dbcve.org
Nx OsOperating system · Cisco

CVE-2021-1229

MEDIUM · 5.3 CVSS v3.1 Published 2021-02-24
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable 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 ICMP Version 6 (ICMPv6) processing in Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a slow system memory leak, which over time could lead to a denial of service (DoS) condition. This vulnerability is due to improper error handling when an IPv6-configured interface receives a specific type of ICMPv6 packet. An attacker could exploit this vulnerability by sending a sustained rate of crafted ICMPv6 packets to a local IPv6 address on a targeted device. A successful exploit could allow the attacker to cause a system memory leak in the ICMPv6 process on the device. As a result, the ICMPv6 process could run out of system memory and stop processing traffic. The device could then drop all ICMPv6 packets, causing traffic instability on the device. Restoring device functionality would require a device reboot.

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 · moderate confidence

A memory leak vulnerability exists in Cisco NX-OS Software's ICMPv6 processing due to improper error handling when an IPv6-configured interface receives a specific type of ICMPv6 packet. An attacker sending a sustained rate of crafted ICMPv6 packets to a local IPv6 address can exhaust system memory in the ICMPv6 process, causing it to stop processing traffic and drop all ICMPv6 packets, resulting in traffic instability that requires a device reboot to restore functionality.

MitigationApply the Cisco NX-OS software patch when available. As an interim measure, consider implementing network-level filtering to block unexpected or malformed ICMPv6 packets destined for the device's local IPv6 addresses.

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
Nx OsOperating system
Affected:= 5.2\(1\)sv5\(1.3a\)= 8.4\(3.53\)= 15.1\(2.31\)

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
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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 NX-OS version
    Run 'show version' or 'show version | include NX-OS' to display the installed Cisco NX-OS version
    Affected if The installed version matches 5.2(1)sv5(1.3a), 8.4(3.53), or 15.1(2.31)
  2. Confirm IPv6 is enabled
    Run 'show ipv6 interface' or 'show running-config | include ipv6' to check if IPv6 is configured on any interface
    Affected if IPv6 is configured on one or more interfaces, making the ICMPv6 processing vulnerable to the attack
  3. Verify ICMPv6 is not blocked at network edge
    Review access-control lists (ACLs) or firewall filters applied to inbound interfaces: run 'show access-lists' and inspect for ICMPv6 deny entries
    Affected if There are no ACL entries or filters blocking inbound ICMPv6 traffic from untrusted sources to the device's local IPv6 addresses
  4. Check for ICMPv6 process memory issues
    Run 'show system resources' or 'show process memory' and look for the icmpv6 process memory usage; compare current usage to baseline
    Affected if The icmpv6 process shows abnormally high memory usage or is consuming disproportionate resources
  5. Monitor for ICMPv6 packet drops
    Run 'show interface' or 'show ipv6 traffic' to check for ICMPv6 packet discards and error counters
    Affected if There is a high rate of ICMPv6 packet drops or errors indicating the process may be failing

The device is affected if it runs NX-OS version 5.2(1)sv5(1.3a), 8.4(3.53), or 15.1(2.31) with IPv6 enabled and no inbound ICMPv6 filtering in place.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the Cisco NX-OS software patch when available. As an interim measure, consider implementing network-level filtering to block unexpected or malformed ICMPv6 packets destined for the device's local IPv6 addresses.

Fix this in Nx Os 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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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-2021-1229 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