CVE-2021-1446Network attack vector

Device reload via crafted IPv4 DNS packets

Published Mar 24, 2021 · Updated Nov 8, 2024

Denial of service in the DNS NAT ALG in Cisco IOS XE Software allows remote attackers to reload devices with crafted IPv4 DNS packets. The DNS ALG packet-inspection logic mishandles certain crafted DNS packets, although Cisco has not disclosed the erroneous branch or state transition. Exploitation requires IPv4 traffic traversing a device with NAT and DNS ALG enabled; IPv6 traffic does not reach the flaw.

CVSS severity8.6
High
EPSS probability1.49%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in the DNS NAT ALG in Cisco IOS XE Software allows remote attackers to reload devices with crafted IPv4 DNS packets. The DNS ALG packet-inspection logic mishandles certain crafted DNS packets, although Cisco has not disclosed the erroneous branch or state transition. Exploitation requires IPv4 traffic traversing a device with NAT and DNS ALG enabled; IPv6 traffic does not reach the flaw.

The record

CVE
CVE-2021-1446
Published
Mar 24, 2021
Updated
Nov 8, 2024
Vendor
ClamAV
Product
Cisco IOS XE Software
Classifications
CWE-754, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 24, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 8, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=n/a

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco IOS XE Softwareversion=n/a

Published CVSS scores

8.6Cisco Systems, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.1NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:C

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-754Improper Check for Unusual or Exceptional Conditions
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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