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Ios XeOperating system · Cisco

CVE-2022-20837

HIGH · 8.6 CVSS v3.1 Published 2022-10-10
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
95/100
Remediation priority · Urgent
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 that is used by Network Address Translation (NAT) in Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload. This vulnerability is due to a logic error that occurs when an affected device inspects certain TCP DNS packets. An attacker could exploit this vulnerability by sending crafted DNS packets through the affected device that is performing NAT for DNS packets. A successful exploit could allow the attacker to cause the device to reload, resulting in a denial of service (DoS) condition on the affected device. Note: This vulnerability can be exploited only by sending IPv4 TCP packets through an affected device. This vulnerability cannot be exploited by sending 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 Cisco IOS XE Software's DNS Application Layer Gateway (ALG) functionality used by NAT causes the device to crash and reload when inspecting certain crafted TCP DNS packets. The vulnerability is triggerable remotely by an unauthenticated attacker sending malicious DNS packets through an affected device performing NAT, specifically via IPv4 TCP traffic only.

MitigationApply the Cisco IOS XE software update addressing CVE-2022-20837. Until patches are applied, consider filtering or inspecting DNS traffic at network boundaries, or implementing traffic rate limiting on NAT for DNS packets to reduce exploitability.

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:all versions

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
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/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 Cisco IOS XE is running
    Execute 'show version' or 'show hardware' to identify the operating system and version number. Look for 'IOS XE' in the output.
    Affected if The device is running any version of Cisco IOS XE Software.
  2. Check if NAT is enabled on the device
    Execute 'show ip nat translations' or 'show ip nat statistics' to see if NAT is actively configured and processing translations.
    Affected if NAT is configured and actively translating traffic on the device.
  3. Verify DNS ALG inspection is active
    Check the NAT configuration with 'show running-config | include ip nat' and look for DNS-related inspection or application-layer gateway settings. Also check 'show ip alg' or platform-specific ALG status commands if available.
    Affected if DNS ALG inspection is enabled, which is typically automatic when NAT processes DNS traffic.
  4. Identify if IPv4 TCP DNS traffic passes through NAT
    Review access-logs, NAT translations with 'show ip nat translations', or packet capture to confirm IPv4 TCP DNS traffic is traversing the NAT boundary.
    Affected if IPv4 TCP DNS packets are being processed through the NAT functionality.

The environment is affected if the device runs Cisco IOS XE with NAT enabled and IPv4 TCP DNS traffic is being processed through the NAT ALG functionality.

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

Apply the Cisco IOS XE software update addressing CVE-2022-20837. Until patches are applied, consider filtering or inspecting DNS traffic at network boundaries, or implementing traffic rate limiting on NAT for DNS packets to reduce exploitability.

Recommended fix Moderate confidence

Cisco IOS XE 16.12.1s or later, or 17.3.1 or later (per Cisco advisory cisco-sa-dns-nat-alg-dos-X8gNucD2)

  1. Check the current Cisco IOS XE version using 'show version' command
  2. Reference Cisco Security Advisory cisco-sa-dns-nat-alg-dos-X8gNucD2 for complete fixed release information
  3. Upgrade to a fixed release such as Cisco IOS XE 16.12.1s or later, or 17.3.1 or later per the advisory
  4. After upgrade, verify the fix by confirming the device does not reload when processing crafted TCP DNS packets through NAT
  5. Consider implementing additional ingress filtering on perimeter devices to reduce exposure to malicious DNS packets
Caveat Standard IOS XE upgrade considerations apply - verify hardware compatibility and review release notes for any behavioral changes

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

Fix this in Ios Xe Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,840
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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-2022-20837 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