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Ios XeOperating system · Cisco

CVE-2018-0476

MEDIUM · 5.9 CVSS v3.0 Published 2018-10-05
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

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 · unedited
A vulnerability in the Network Address Translation (NAT) Session Initiation Protocol (SIP) Application Layer Gateway (ALG) of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload. The vulnerability is due to improper processing of SIP packets in transit while NAT is performed on an affected device. An unauthenticated, remote attacker could exploit this vulnerability by sending crafted SIP packets via UDP port 5060 through an affected device that is performing NAT for SIP packets. A successful exploit could allow an attacker to cause the device to reload, resulting in a denial of service (DoS) condition.

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 confidence

A vulnerability in the NAT Session Initiation Protocol (SIP) Application Layer Gateway (ALG) of Cisco IOS XE Software allows an unauthenticated remote attacker to cause device reload by sending specially crafted SIP packets through an affected device performing NAT. The vulnerability stems from improper processing of SIP packets in transit while NAT is performed.

MitigationApply Cisco security updates for CVE-2018-0476 when available; consider filtering or blocking UDP port 5060 SIP traffic at network boundaries if immediate patching is not possible.

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
Affected:= 15.5\(3\)s5.1= 15.5\(3\)s6.1= 16.6.2

CVSS 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
None
Integrity
None
Availability
High

CVSS:3.0/AV:N/AC:H/PR:N/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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify the Cisco IOS XE version
    Run the command 'show version' and locate the version string in the output (typically labeled as 'Version' or part of the system image name)
    Affected if The version displayed matches 15.5(3)S5.1, 15.5(3)S6.1, or 16.6.2 exactly
  2. Verify NAT is enabled on the device
    Run 'show running-config | include ip nat' or check the configuration for any 'ip nat' entries, or use 'show ip nat statistics'
    Affected if NAT is configured and active on the device
  3. Confirm SIP ALG processing is occurring
    Check configuration for 'ip nat service sip' or verify SIP traffic (UDP port 5060) is traversing the NAT boundary by reviewing 'show ip nat translations' or logging
    Affected if SIP traffic is being processed through the NAT ALG (SIP packets in UDP/5060 are flowing through the device)
  4. Verify the device is performing NAT for SIP traffic
    Run 'show ip nat translations' and look for SIP-related entries, or monitor traffic on UDP port 5060 while NAT is active
    Affected if SIP packets are being translated by the NAT ALG on the affected device

The device is affected if it runs Cisco IOS XE version 15.5(3)S5.1, 15.5(3)S6.1, or 16.6.2 AND has NAT enabled with SIP traffic traversing through the NAT ALG.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply Cisco security updates for CVE-2018-0476 when available; consider filtering or blocking UDP port 5060 SIP traffic at network boundaries if immediate patching is not possible.

Fix this in Ios Xe Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2018-0476 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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