iOSOperating system · Cisco
CVE-2018-0174
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 · uneditedA 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 the affected device to reload, resulting in a DoS condition. Cisco Bug IDs: CSCuh91645.
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 confidenceA vulnerability in Cisco IOS/IOS XE DHCP option 82 encapsulation performs incomplete input validation on option 82 information received in DHCPv4 packets from DHCP relay agents, allowing an unauthenticated remote attacker to cause the affected device to reload, resulting in denial of service.
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
= 12.2\(33\)sre7a<= 15.2\(4a\)ea5<= 15.2\(6\)e0a
Ios XeOperating system
= 12.2\(33\)sre7a<= 15.2\(4a\)ea5<= 15.2\(6\)e0aCVSS 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 checksWork through these to decide whether this CVE applies to you.
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Identify the Cisco IOS or IOS XE versionExecute 'show version' on the device CLI and note the exact version number (e.g., 15.2(4)E, 12.2(33)SRE, etc.)Affected if The installed version matches or falls within: 12.2(33)SRE7a, any 15.2(4) release up to and including 15.2(4a)EA5, or any 15.2(6) release up to and including 15.2(6)E0a. Versions outside these ranges are not affected.
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Determine if DHCP relay is enabledRun 'show ip interface' on relevant interfaces or check the configuration with 'show running-config | include ip helper-address' to see if the device is acting as a DHCP relayAffected if The device has 'ip helper-address' configured on any interface, indicating it is functioning as a DHCP relay agent. Without DHCP relay enabled, the attack surface does not exist.
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Verify DHCP option 82 processing is activeCheck the DHCP relay configuration with 'show ip dhcp relay' or examine the running config for 'ip dhcp relay information option' or 'ip dhcp relay information policy' commandsAffected if Option 82 insertion, removal, or relay-advanced is explicitly configured. The vulnerability exploits incomplete validation of option 82 data in DHCPv4 packets, so option 82 handling must be enabled for exploitation.
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Confirm the device processes DHCPv4 traffic from untrusted sourcesReview interface configurations and ACLs to determine if the device accepts DHCPv4 packets from external or untrusted networks without strict validationAffected if The device accepts DHCPv4 relay traffic from network segments that are not fully trusted (e.g., customer-facing VLANs, DMZ, or upstream networks), creating the attack vector.
A device is likely affected if it runs a vulnerable IOS/IOS XE version (within the 12.2(33)SRE7a or 15.2(4a)EA5/15.2(6)E0a ranges) AND has DHCP relay with option 82 handling enabled, as the vulnerability is triggered specifically by malformed option 82 data in relayed DHCPv4 packets.
Generated from the published advisory. Verify against your own configuration.
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 dataApply the Cisco patch for this vulnerability (CSCuh91645). If patching is immediately impractical, consider disabling DHCP option 82 encapsulation on affected interfaces or implementing network filtering to reject malformed DHCPv4 packets at perimeter points.
Fix this in iOS
Exploited in the wild — priority engagement
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,600.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2018-0174 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2018-0174 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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