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Ios XeOperating system · Cisco

CVE-2017-3859

HIGH · 7.5 CVSS v3.0 Published 2017-03-22
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
A vulnerability in the DHCP code for the Zero Touch Provisioning feature of Cisco ASR 920 Series Aggregation Services Routers could allow an unauthenticated, remote attacker to cause an affected device to reload. The vulnerability is due to a format string vulnerability when processing a crafted DHCP packet for Zero Touch Provisioning. An attacker could exploit this vulnerability by sending a specially crafted DHCP packet to an affected device. An exploit could allow the attacker to cause the device to reload, resulting in a denial of service (DoS) condition. This vulnerability affects Cisco ASR 920 Series Aggregation Services Routers that are running an affected release of Cisco IOS XE Software (3.13 through 3.18) and are listening on the DHCP server port. By default, the devices do not listen on the DHCP server port. Cisco Bug IDs: CSCuy56385.

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 format string vulnerability in the DHCP code for Zero Touch Provisioning on Cisco ASR 920 Series routers running IOS XE 3.13-3.18 allows an unauthenticated remote attacker to send a specially crafted DHCP packet causing the device to reload, resulting in denial of service.

MitigationEnsure the DHCP server port is not exposed on affected devices (disabled by default). Apply the Cisco vendor patch/firmware update to address the format string vulnerability in the DHCP processing code.

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:= 3.13.4s= 3.13.5as= 3.13.5s= 3.13.6as= 3.13.6s= 3.14.3s= 3.14.4s= 3.15.2s= 3.15.3s= 3.15.4s= 3.16.0cs= 3.16.0s

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 device model
    Run 'show version' or 'show inventory' and look for ASR 920 in the output
    Affected if Device is not a Cisco ASR 920 Series router - not affected
  2. Verify IOS XE version
    Run 'show version' and locate the IOS XE software version string (for example, 3.13.5s, 3.14.3s, 3.16.0s)
    Affected if Version matches one of these: 3.13.4s, 3.13.5as, 3.13.5s, 3.13.6as, 3.13.6s, 3.14.3s, 3.14.4s, 3.15.2s, 3.15.3s, 3.15.4s, 3.16.0cs, 3.16.0s - potentially affected
  3. Confirm Zero Touch Provisioning is enabled
    Run 'show zerotouch' and check the ZTP status. Alternatively, check configuration for 'zerotouch' commands under the device configuration
    Affected if ZTP is active or configured - potentially affected if DHCP is also exposed
  4. Verify DHCP server is exposed
    Run 'show ip dhcp import' or 'show running-config | include ip dhcp' to check if DHCP server features are enabled. Also check interface configurations for DHCP-related service bindings
    Affected if DHCP server is enabled or the DHCP port is exposed on any interface - likely affected when combined with vulnerable version and ZTP

Device is affected if it is an ASR 920 running a listed IOS XE version with Zero Touch Provisioning enabled AND the DHCP server port is exposed (non-default state).

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

Ensure the DHCP server port is not exposed on affected devices (disabled by default). Apply the Cisco vendor patch/firmware update to address the format string vulnerability in the DHCP processing code.

Fix this in Ios Xe Scoped from the published advisory
  • Consultation4.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,480
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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-2017-3859 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
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  • Version or environment caveats, and links to real fixes
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