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Ios XeOperating system · Cisco

CVE-2021-1446

HIGH · 7.5 CVSS v3.1 Published 2021-03-24
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
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 the DNS application layer gateway (ALG) functionality used by Network Address Translation (NAT) in Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload. The vulnerability is due to a logic error that occurs when an affected device inspects certain DNS packets. An attacker could exploit this vulnerability by sending crafted DNS packets through an affected device that is performing NAT for DNS packets. A successful exploit could allow an attacker to cause the device to reload, resulting in a denial of service (DoS) condition on an affected device. The vulnerability can be exploited only by traffic that is sent through an affected device via IPv4 packets. The vulnerability cannot be exploited via IPv6 traffic.

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 logic error in the DNS Application Layer Gateway (ALG) within Cisco IOS XE Software's NAT functionality allows an unauthenticated remote attacker to cause device reload by sending crafted DNS packets through an affected device performing NAT. The vulnerability is exploitable only via IPv4 traffic and results in denial of service.

MitigationApply the appropriate Cisco IOS XE software update (refer to Cisco security advisory) and coordinate a maintenance window. As a workaround, consider implementing ACLs to filter suspicious DNS traffic or disable DNS ALG if operationally feasible.

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:= 3.7.0bs= 3.7.0s= 3.7.0xas= 3.7.0xbs= 3.7.1as= 3.7.1s= 3.7.2s= 3.7.2ts= 3.7.3s= 3.7.4as= 3.7.4s= 3.7.5s

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
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 checks

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

  1. Identify the device OS and version
    Execute 'show version' on the device CLI to retrieve the IOS XE version string
    Affected if The displayed version matches one of: 3.7.0bs, 3.7.0s, 3.7.0xas, 3.7.0xbs, 3.7.1as, 3.7.1s, 3.7.2s, 3.7.2ts, 3.7.3s, 3.7.4as, 3.7.4s, or 3.7.5s
  2. Confirm NAT is configured
    Execute 'show ip nat translations' or 'show running-config | include ip nat' to verify NAT is actively configured on the device
    Affected if NAT is enabled and there are active translations or NAT configuration present in the running config
  3. Verify DNS ALG is enabled
    Execute 'show service internal | include DNS ALG' or check the NAT configuration for ALG inspection rules using 'show running-config | include alg'
    Affected if DNS Application Layer Gateway (ALG) inspection is enabled in the device configuration
  4. Confirm IPv4 NAT processing is active
    Check for IPv4 NAT activity using 'show ip nat statistics' or monitor IPv4 traffic passing through the NAT interface
    Affected if The device is performing NAT translation on IPv4 traffic and DNS packets could traverse the NAT boundary
  5. Review recent device reload history
    Check logs and 'show logging' output for unexpected reloads or crashinfo files that may indicate exploitation attempts
    Affected if The device has experienced unexplained reloads or crashes that coincide with DNS traffic passing through NAT

The device is affected if it runs any of the listed IOS XE versions, has NAT enabled with DNS ALG inspection active, and processes IPv4 traffic through the NAT function.

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 appropriate Cisco IOS XE software update (refer to Cisco security advisory) and coordinate a maintenance window. As a workaround, consider implementing ACLs to filter suspicious DNS traffic or disable DNS ALG if operationally feasible.

Fix this in Ios Xe Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,440
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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-2021-1446 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
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