Threats / Cisco / CVE-2018-0172

CVE-2018-0172 · EUVD no mirror located · GCVE no mirror located Verified 2026-09-19

Cisco IOS and XE Software vulnerability

A vulnerability in DHCP option 82 encapsulation in Cisco IOS and IOS XE Software allows denial-of-service attacks through malformed DHCP packets.

Verdict

Today item — known-exploited.

An attacker can send specially crafted DHCP packets to trigger a denial-of-service condition on affected Cisco network devices. This vulnerability has been exploited in the wild and requires network access to the DHCP service.

CISA KEV Yes · 2022-03-03⁵EPSS 0.0782 (verify live)⁶CVSS 8.6 (CISA)⁴CISA SSVC Exploitation: active · Automatable: no · Impact: total⁴

Is it exploitable?

— the evidence, ranked above the score

Reported exploitation

2 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.

cisa.gov ↗cisco.com ↗Confirmed

Exploited in the wild

Listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-03-03).

CISA KEV ↗Confirmed

Probability (EPSS)

EPSS 0.0782 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.

FIRST EPSS ↗High

Severity / affected

CVSS 8.6 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H) · Affected: Cisco, IOS and IOS XE Software. Confirm exact fixed builds in the vendor advisory.CVSS — CISA-assigned via the ADP container (CVE.org), version 3.1; the CNA left no metrics, so CISA's own score is used ahead of NVD.

CISA-ADP ↗Reported

Weakness (CWE)

Mapped to CWE-20 Improper Input Validation.CWE — CNA-assigned (CVE.org); the weakness class drives how the flaw is exploited.

CVE.org ↗Reported

CISA SSVC (triage disposition)

Exploitation: active · Automatable: no · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.

CISA-ADP ↗Reported

Currency of the record

CISA added this to its KEV catalog 1436 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.

CISA KEV ↗CVE.org ↗Reported

WeaknessCWE-20 · Improper Input Validation

Who’s exploiting it?

— attribution turns risk into urgency

Attribution not established

No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.

Why it matters

— the attack path, told twice: adversary, then board

Front door — unauthenticated access narrative 1

Attacker

I craft a malformed DHCP packet with invalid option 82 encapsulation data.

Business

Network availability is disrupted as the device becomes unresponsive or crashes.

Keys to the kingdom — privilege/identity takeover narrative 2

Attacker

I send the malicious packet to the target Cisco device on the network.

Business

Critical routing or switching infrastructure fails, causing widespread connectivity loss.

Lateral reach — past segmentation narrative 3

Attacker

I repeat or automate the attack to maintain the denial-of-service condition.

Business

Extended outage increases incident response costs and damages customer trust.

What to do

— defensible action

Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.¹

Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.

Coverage & confidence

— what we know, and what we don’t

Established (cited)

KEV listing (CISA)

EPSS probability (FIRST)

2 reported-exploitation source(s)

CVSS 8.6 — CISA-assigned (CVE.org ADP)

CISA SSVC triage disposition (CVE.org ADP)

CWE weakness mapping — CNA-assigned (CVE.org)

Catalogued by cisco (CNA)

Named finder/reporter credit (CVE.org)

Coverage gaps — stated, not hidden

No EUVD / GCVE mirror in feed — single-authority dependency for the identifier.

EPSS & exposure are time-varying; verify live at the source.

Threat-actor attribution not established from feed data — absence of a name is not absence of compromise.

Disclosure & credit²

Catalogued by ciscoCNA

Credited with finding itTenablefinder

Found an error? Propose a correction.

A correction is a cited counter-claim — it must cite a source, gets reviewed by a second human, and is never auto-applied. See the correction convention and our identity npub1j7gt9ky7sfcrjn8jjee6693dkzvk4rahs0fk2suu7968dfns62zs3mqm3y.

With JavaScript off: publish a signed kind 1111 Nostr event tagging ["r", "https://basicsecurity.net/threat/cve-2018-0172.html"], ["v", "sha256:e8060c7bbb1fa0695cc46e27226e8690edac297544197bf7f771d9839207a9ee"] (the record version), plus ["src", "<your source URL>"] and ["t", "correction"], per the correction convention. Our identity: npub1j7gt9ky7sfcrjn8jjee6693dkzvk4rahs0fk2suu7968dfns62zs3mqm3y. Cite-or-die: an event with no src is a coverage finding, not a proposal.