iOSOperating system · Cisco

CVE-2014-3347

MEDIUM · 5.4 CVSS v2.0 Published 2014-08-28

Mitigation only

No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.

See remediation →

63/100

Remediation priority · Elevated

Remotely reachable No privileges Zero-click

Official description

NVD · unedited

Cisco IOS 15.1(4)M2 on Cisco 1800 ISR devices, when the ISDN Basic Rate Interface is enabled, allows remote attackers to cause a denial of service (device hang) by leveraging knowledge of the ISDN phone number to trigger an interrupt timer collision during entropy collection, leading to an invalid state of the hardware encryption module, aka Bug ID CSCul77897.

Technical summary

dbcve analysis · moderate confidence

Remote attackers with knowledge of the ISDN phone number can trigger an interrupt timer collision during entropy collection on affected Cisco 1800 ISR devices running IOS 15.1(4)M2 with ISDN Basic Rate Interface enabled. This causes the hardware encryption module to enter an invalid state, resulting in device hang and denial of service.

MitigationIf ISDN BRI is not required, disable it via IOS configuration. Otherwise, apply Cisco IOS updates addressing CSCul77897 when available, and consider network segmentation to limit exposure of ISDN phone numbers.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions

NVD · CPE data

iOSOperating system

Affected:= 15.1$4$m2

1801 Integrated Service RouterHardware / appliance

Affected:all versions

1802 Integrated Service RouterHardware / appliance

Affected:all versions

1803 Integrated Service RouterHardware / appliance

Affected:all versions

1811 Integrated Service RouterHardware / appliance

Affected:all versions

1812 Integrated Service RouterHardware / appliance

Affected:all versions

1841 Integrated Service RouterHardware / appliance

Affected:all versions

1861 Integrated Service RouterHardware / appliance

Affected:all versions

CVSS breakdown

From the vector

Attack vector: Network
Complexity: High
Authentication: None
Confidentiality: None
Integrity: None
Availability: Complete

AV:N/AC:H/Au:N/C:N/I:N/A:C

Am I affected?

dbcve checks

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

Identify the router model

Execute 'show version' or 'show inventory' and look for the hardware model in the output (e.g., Cisco 1801, 1802, 1803, 1811, 1812, 1841, or 1861 Integrated Service Router)

Affected if The device is not one of the listed Cisco 1800 series ISR models (1801, 1802, 1803, 1811, 1812, 1841, 1861)
Check the IOS version

Execute 'show version' and locate the 'IOS' or 'Version' line in the output

Affected if The IOS version is 15.1(4)M2, or the device is any 1801/1802/1803/1811/1812/1841/1861 model running any IOS version (these are listed as 'all versions')
Verify ISDN BRI is configured

Execute 'show running-config | include isdn' or 'show running-config | include BRI' to search for ISDN Basic Rate Interface configuration

Affected if ISDN BRI configuration appears in the running config (lines containing 'isdn switch-type' or 'interface BRI' are present)
Confirm ISDN BRI interface is active

Execute 'show interface bri0/0/0' (or 'show interface bri0/0/1' if applicable) and check for 'line protocol' status, or run 'show isdn status' to see interface state

Affected if The BRI interface shows as 'up' with line protocol up, or 'show isdn status' displays active ISDN connections

The device is affected if it is a Cisco 1800 series ISR (1801-1803, 1811-1812, 1841, 1861) running the vulnerable IOS version (15.1(4)M2 or any version for most models) AND ISDN BRI is enabled and active.

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

Remediation

From vendor data

Mitigation available No clean upgrade yet — mitigate in the meantime

Mitigation

If ISDN BRI is not required, disable it via IOS configuration. Otherwise, apply Cisco IOS updates addressing CSCul77897 when available, and consider network segmentation to limit exposure of ISDN phone numbers.

Fix this in iOS Scoped from the published advisory

Consultation2.0 h
Implementation2.0 h
Testing2.0 h
Review / QA1.0 h

7.0 hours of engineering $1,240

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Scan for this in your stack

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References

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2014-3347 in production — separate from our analysis above.

Notes0 Guidelines

Know something about CVE-2014-3347?

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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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

At a glance

A fix existsA vendor remedy is published

Severity 5.4 Medium

Exploit likelihood EPSS, next 30 days 1.0%

Affects: iOS

Remediation

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Fix this in iOS 7 hrs · Moderate

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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.

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.

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.

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.

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.

Check your environment

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.

Scan for this in your stack

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Practitioner notes

No notes yet

Official description

Technical summary

Affected products & versions

CVSS breakdown

Am I affected?

Remediation

References