Ios XeOperating system · Cisco
CVE-2018-0189
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 Forwarding Information Base (FIB) code of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, network attacker to cause a denial of service (DoS) condition. The vulnerability is due to a limitation in the way the FIB is internally representing recursive routes. An attacker could exploit this vulnerability by injecting routes into the routing protocol that have a specific recursive pattern. The attacker must be in a position on the network that provides the ability to inject a number of recursive routes with a specific pattern. An exploit could allow the attacker to cause an affected device to reload, creating a DoS condition. Cisco Bug IDs: CSCva91655.
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 the Forwarding Information Base (FIB) of Cisco IOS and IOS XE Software allows an unauthenticated network attacker to cause denial of service by injecting routes with a specific recursive pattern. The flaw stems from a limitation in how the FIB internally represents recursive routes, causing the affected device to reload when exploited.
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
< 15.5\(3\)s5< 15.5\(3\)m5< 15.4\(3\)s7< 15.4\(2\)s1< 15.4\(1\)s1< 15.4\(1\)s0a< 15.2\(5\)e1< 15.2\(4\)e5< 15.2\(2\)e1< 15.2\(1\)e1CVSS 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
- High
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/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 Cisco IOS/IOS XE versionRun 'show version' command and look for the software version string (e.g., 15.4(3)S7, 15.2(5)E1)Affected if The installed version matches one of the affected ranges: < 15.5(3)s5, < 15.5(3)m5, < 15.4(3)s7, < 15.4(2)s1, < 15.4(1)s1, < 15.4(1)s0a, < 15.2(5)e1, < 15.2(4)e5, < 15.2(2)e1, or < 15.2(1)e1
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Examine FIB for recursive routesRun 'show ip route recursive' or 'show ip fib' and inspect the routing table for routes that point to other routes (recursive lookups)Affected if The FIB contains routes with recursive next-hop patterns that could trigger the limitation in FIB recursive route representation
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Check for unexpected device reloadsReview logs with 'show log' or 'show reload' and look for unexplained reload reasons or crash filesAffected if The device has experienced unexplained reloads or crashes, especially after receiving route updates from untrusted sources
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Identify routing protocol peersRun 'show ip protocols summary' or check routing protocol neighbor tables to list all peers injecting routes into the deviceAffected if The device accepts route updates from untrusted or unauthenticated peering devices without route filtering or protocol authentication (e.g., no MD5 authentication on BGP/OGRP)
You are affected if your device runs an affected Cisco IOS/IOS XE version AND processes recursive routes from untrusted sources, as indicated by unexpected reloads or the presence of recursive route patterns in the FIB.
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 data15.215.415.5
Apply the Cisco software update corresponding to bug ID CSCva91655. Additionally, implement route filtering and authentication on routing protocols to prevent unauthorized route injection from untrusted sources.
Fix this in Ios Xe
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing4.0 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 $5,120.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2018-0189 — 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-2018-0189 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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- Version or environment caveats, and links to real fixes
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