iOSOperating system · Cisco
CVE-2018-0131
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 implementation of RSA-encrypted nonces in Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to obtain the encrypted nonces of an Internet Key Exchange Version 1 (IKEv1) session. The vulnerability exists because the affected software responds incorrectly to decryption failures. An attacker could exploit this vulnerability sending crafted ciphertexts to a device configured with IKEv1 that uses RSA-encrypted nonces. A successful exploit could allow the attacker to obtain the encrypted nonces. Cisco Bug IDs: CSCve77140.
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 and IOS XE Software allows an unauthenticated remote attacker to obtain encrypted nonces from IKEv1 sessions that use RSA-encrypted nonces. The flaw stems from incorrect responses to decryption failures when processing crafted ciphertexts, potentially exposing sensitive key exchange material.
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
= 15.5\(3\)s
Ios XeOperating system
= 15.5\(3\)sCVSS 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
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
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' on the device and locate the version string in the outputAffected if The version is 15.5(3)s or earlier (any version matching or prior to 15.5(3)s)
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Confirm IKEv1 is enabledRun 'show crypto isakmp sa' and 'show crypto isakmp policy' to list active IKEv1 security associations and configured ISAKMP policiesAffected if Any IKEv1 policies are configured or active IKEv1 sessions exist
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Verify RSA-encrypted nonce is in useRun 'show crypto isakmp policy' and examine the authentication method in each ISAKMP policy configurationAffected if Any ISAKMP policy shows 'rsa-encrypt' or 'rsa-encryption' as the authentication method (indicating RSA-encrypted nonces are enabled)
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Check IKEv1 accessibilityRun 'show access-lists' and verify whether ACLs permit IKEv1 traffic (UDP port 500) from untrusted sourcesAffected if IKEv1 traffic is permitted from any network that includes untrusted or external addresses
The environment is affected if the device runs Cisco IOS or IOS XE version 15.5(3)s or earlier AND has IKEv1 configured with RSA-encrypted nonces and accessible to the attacker.
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 relevant Cisco IOS/IOS XE software update from CSCve77140. If immediate patching is not possible, consider disabling IKEv1 or restricting IKEv1 access to trusted networks using access control lists.
Fix this in iOS
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-2018-0131 — 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-2018-0131 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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