CVE-2022-20837Network attack vector

Device reload via malformed TCP DNS inspection

Published Oct 10, 2022 · Updated Nov 1, 2024

Denial of service in Cisco IOS XE Software allows remote attackers to reload affected devices via crafted IPv4 TCP DNS packets. The DNS ALG used by NAT makes a logic error while inspecting certain TCP DNS packets, causing the device to reload rather than safely reject them. Exploitation is unauthenticated and requires traffic to transit an affected ESP 100-X, ESP 200-X, C8500-12X4QC, or C8500-12X device with NAT active and TCP DNS ALG enabled.

CVSS severity8.6
High
EPSS probability0.94%
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 Cisco IOS XE Software allows remote attackers to reload affected devices via crafted IPv4 TCP DNS packets. The DNS ALG used by NAT makes a logic error while inspecting certain TCP DNS packets, causing the device to reload rather than safely reject them. Exploitation is unauthenticated and requires traffic to transit an affected ESP 100-X, ESP 200-X, C8500-12X4QC, or C8500-12X device with NAT active and TCP DNS ALG enabled.

The record

CVE
CVE-2022-20837
Published
Oct 10, 2022
Updated
Nov 1, 2024
Vendor
ClamAV
Product
Cisco IOS XE Software
Classifications
CWE-754, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 10, 2022CVE publishedPublication date reported by the CVE source.
  2. Nov 1, 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?

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  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

8.6CiscoCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X

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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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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