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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 17 Mar 2022.
iOSOperating system · Cisco

CVE-2018-0172

HIGH · 8.6 CVSS v3.1 Published 2018-03-28
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
In the wild 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 DHCP option 82 encapsulation functionality of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. The vulnerability exists because the affected software performs incomplete input validation of option 82 information that it receives in DHCP Version 4 (DHCPv4) packets from DHCP relay agents. An attacker could exploit this vulnerability by sending a crafted DHCPv4 packet to an affected device. A successful exploit could allow the attacker to cause a heap overflow condition on the affected device, which will cause the device to reload and result in a DoS condition. Cisco Bug IDs: CSCvg62730.

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 heap overflow vulnerability exists in Cisco IOS and IOS XE Software's DHCP option 82 encapsulation functionality due to incomplete input validation of option 82 information in DHCPv4 packets from relay agents. An unauthenticated remote attacker can send a crafted DHCPv4 packet to trigger the heap overflow, causing the affected device to reload and result in denial of service.

MitigationApply the Cisco patch for bug CSCvg62730 by upgrading to a fixed software version. As an interim measure, consider disabling DHCP relay or implementing ACLs to filter untrusted DHCP traffic at network boundaries.

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
iOSOperating system
Affected:all versions
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 device runs Cisco IOS or IOS XE
    Use 'show version' command to identify the operating system. Look for 'Cisco IOS' or 'Cisco IOS XE' in the output.
    Affected if Device runs any version of Cisco IOS or IOS XE software (all versions are affected per the advisory).
  2. Check if DHCP relay is enabled
    Run 'show ip interface' on relevant interfaces or use 'show running-config | include ip helper-address' to see if DHCP relay is configured.
    Affected if DHCP relay is configured via 'ip helper-address' command, indicating the device may process DHCP packets.
  3. Verify DHCP option 82 insertion is configured
    Run 'show running-config | include ip dhcp relay information option' or check DHCP relay configuration for 'ip dhcp relay information option' settings.
    Affected if DHCP option 82 insertion is explicitly enabled via 'ip dhcp relay information option' or 'ip dhcp relay information option enable' configuration.
  4. Check for trusted/untrusted DHCP relay interfaces
    Run 'show ip interface' on upstream/downstream interfaces and check for 'ip dhcp relay information trusted' or 'ip dhcp relay information untrusted' settings.
    Affected if Interfaces are configured as trusted for DHCP relay with option 82, allowing option 82 data to be processed without validation.

A Cisco IOS or IOS XE device is affected if it has DHCP relay configured with option 82 insertion or trusted option 82 processing enabled, regardless of version.

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 patch for bug CSCvg62730 by upgrading to a fixed software version. As an interim measure, consider disabling DHCP relay or implementing ACLs to filter untrusted DHCP traffic at network boundaries.

Fix this in iOS Exploited in the wild — priority engagement
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2018-0172 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