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Nx OsOperating system · Cisco

CVE-2015-6393

HIGH · 7.5 CVSS v3.0 Published 2016-10-06
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
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
Cisco NX-OS 4.1 through 7.3 and 11.0 through 11.2 on Nexus 2000, 3000, 3500, 5000, 5500, 5600, 6000, 7000, 7700, and 9000 devices allows remote attackers to cause a denial of service (device crash) via malformed IPv4 DHCP packets to the DHCPv4 relay agent, aka Bug IDs CSCuq39250, CSCus21733, CSCus21739, CSCut76171, and CSCux67182.

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

The vulnerability is in the DHCPv4 relay agent component of Cisco NX-OS. Remote unauthenticated attackers can send malformed IPv4 DHCP packets to the DHCP relay to trigger a device crash, causing complete denial of service.

MitigationApply Cisco NX-OS patches addressing the specific bug IDs (CSCuq39250, CSCus21733, CSCus21739, CSCut76171, CSCux67182) per the Cisco security advisory; alternatively, filter malformed DHCP traffic at network perimeter devices as a compensating control.

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
Nx OsOperating system
Affected:= 4.2\(1\)n1\(1\)= 4.2\(1\)n2\(1\)= 4.2\(1\)n2\(1a\)= 5.0\(2\)n1\(1\)= 5.0\(2\)n2\(1\)= 5.0\(2\)n2\(1a\)= 5.0\(3\)n1\(1c\)= 5.0\(3\)n2\(1\)= 5.0\(3\)n2\(2\)= 5.0\(3\)n2\(2a\)= 5.0\(3\)n2\(2b\)= 5.1\(3\)n1\(1\)

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
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.0/AV:N/AC:L/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 installed NX-OS version
    Run 'show version' on the device and locate the NX-OS release line (e.g., 'NX-OSv 5.0(3)n2(2)' or similar)
    Affected if The version matches exactly one of these: 4.2(1)n1(1), 4.2(1)n2(1), 4.2(1)n2(1a), 5.0(2)n1(1), 5.0(2)n2(1), 5.0(2)n2(1a), 5.0(3)n1(1c), 5.0(3)n2(1), 5.0(3)n2(2), 5.0(3)n2(2a), 5.0(3)n2(2b), 5.1(3)n1(1)
  2. Verify DHCP relay feature is enabled
    Run 'show feature | include dhcp' to check if the DHCP relay feature is turned on
    Affected if The output shows dhcp_relay as enabled (status = enabled)
  3. Confirm DHCP relay is configured on an interface
    Run 'show running-config | include relay' or 'show ip helper-address' to see if DHCP relay is actively configured on any interface
    Affected if Interfaces are configured with DHCP relay helper addresses or relay statements (ip helper-address commands)
  4. Review recent crash logs for DHCP-related causes
    Run 'show logging logfile | include DHCP' or 'show process log' to look for recent crash indicators related to DHCP processing
    Affected if Recent crash logs reference DHCP relay or packet processing failures with timestamps matching recent activity

The device is vulnerable only if it runs an exact affected version AND has the DHCP relay feature enabled AND is actively using DHCP relay configuration.

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 NX-OS patches addressing the specific bug IDs (CSCuq39250, CSCus21733, CSCus21739, CSCut76171, CSCux67182) per the Cisco security advisory; alternatively, filter malformed DHCP traffic at network perimeter devices as a compensating control.

Fix this in Nx Os Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing6.0 h
  • Review / QA3.0 h
27.0 hours of engineering $4,800
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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-2015-6393 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
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data