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FxosOperating system · Cisco

CVE-2021-34714

HIGH · 7.4 CVSS v3.1 Published 2021-09-23
Fix available
A fix is available. Upgrade to 2.2.2.148 / 2.3.1.216 or later.
See remediation →
79/100
Remediation priority · High
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 Unidirectional Link Detection (UDLD) feature of Cisco FXOS Software, Cisco IOS Software, Cisco IOS XE Software, Cisco IOS XR Software, and Cisco NX-OS Software could allow an unauthenticated, adjacent attacker to cause an affected device to reload. This vulnerability is due to improper input validation of the UDLD packets. An attacker could exploit this vulnerability by sending specifically crafted UDLD packets to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a denial of service (DoS) condition. Note: The UDLD feature is disabled by default, and the conditions to exploit this vulnerability are strict. An attacker must have full control of a directly connected device. On Cisco IOS XR devices, the impact is limited to the reload of the UDLD process.

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 Unidirectional Link Detection (UDLD) feature across Cisco FXOS, IOS, IOS XE, IOS XR, and NX-OS Software allows an unauthenticated, adjacent attacker to cause device reload via specially crafted UDLD packets due to improper input validation. The attacker must have full control of a directly connected device to exploit this. UDLD is disabled by default.

MitigationKeep UDLD disabled if not required; if enabled, apply Cisco vendor patches and ensure physical security of directly connected network devices.

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
FxosOperating system
Affected:>= 2.2, < 2.2.2.148>= 2.3, < 2.3.1.216>= 2.4, < 2.4.1.273>= 2.6, < 2.6.1.224>= 2.7, < 2.7.1.143>= 2.8, < 2.8.1.143>= 2.9, < 2.9.1.135
Firepower Extensible Operating SystemOperating system
Affected:<= 8.4\(3.115\)<= 7.0\(3\)i7\(9\)<= 7.3\(8\)n1\(1\)<= 3.2\(3o\)a<= 4.1\(1a\)a
iOSOperating system
Affected:<= 8.4\(3.115\)<= 7.0\(3\)i7\(9\)<= 7.3\(8\)n1\(1\)<= 3.2\(3o\)a<= 4.1\(1a\)a
Ios XeOperating system
Affected:<= 8.4\(3.115\)<= 7.0\(3\)i7\(9\)<= 7.3\(8\)n1\(1\)<= 3.2\(3o\)a<= 4.1\(1a\)a
Ios XrOperating system
Affected:<= 8.4\(3.115\)<= 7.0\(3\)i7\(9\)<= 7.3\(8\)n1\(1\)<= 3.2\(3o\)a<= 4.1\(1a\)a
Nx OsOperating system
Affected:<= 8.4\(3.115\)<= 7.0\(3\)i7\(9\)<= 7.3\(8\)n1\(1\)<= 3.2\(3o\)a

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
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/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. Verify if UDLD is enabled globally
    Run 'show udld global' or 'show udld' to see if UDLD is globally enabled on the device
    Affected if UDLD is globally enabled (UDLD must be turned on for the vulnerability to be exploitable)
  2. Check UDLD status on individual interfaces
    Run 'show udld interface <interface-id>' or 'show interface' with UDLD status for each interface to identify any ports with UDLD enabled
    Affected if Any interface has UDLD enabled in aggressive or normal mode
  3. Identify the device software version
    Run 'show version' to display the installed OS version and compare against the affected product version ranges provided in the CVE
    Affected if The software version falls within any of the listed affected version ranges
  4. Match version against FXOS affected ranges
    For Cisco FXOS/Firepower, verify version is >= 2.2 and < 2.2.2.148; or >= 2.3 and < 2.3.1.216; or >= 2.4 and < 2.4.1.273; or >= 2.6 and < 2.6.1.224; or >= 2.7 and < 2.7.1.143; or >= 2.8 and < 2.8.1.143; or >= 2.9 and < 2.9.1.135
    Affected if FXOS version matches any of these ranges
  5. Match version against IOS/IOS-XE/NX-OS affected ranges
    For Cisco IOS, IOS XE, IOS XR, or NX-OS, verify version is <= 8.4(3.115); <= 7.0(3)i7(9); <= 7.3(8)n1(1); <= 3.2(3o)a; or <= 4.1(1a)a
    Affected if The IOS/IOS-XE/IOS-XR/NX-OS version matches any of these ranges

You are affected only if UDLD is currently enabled on the device AND the software version falls within the listed affected version ranges; if UDLD is disabled (the default), the device is not vulnerable despite the version.

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.

dbcve · scoped
Upgrade available Upgrade to 2.2.2.148 / 2.3.1.216 / 2.4.1.273 or later
Fixed in 2.2.2.1482.3.1.2162.4.1.273
Interim mitigation

Keep UDLD disabled if not required; if enabled, apply Cisco vendor patches and ensure physical security of directly connected network devices.

Recommended fix High confidence

FXOS 2.2.2.148+, 2.3.1.216+, 2.4.1.273+, or 2.6.1.224+; IOS/IOS XE/IOS XR/NX-OS: next maintenance release beyond 8.4(3.115)/7.0(3)i7(9)/7.3(8)n1(1)/3.2(3o)a per Cisco advisory

  1. 1. Identify the specific Cisco product platform (FXOS, IOS, IOS XE, IOS XR, NX-OS, or Firepower) in use
  2. 2. Determine the current installed version using 'show version' command
  3. 3. For FXOS 2.2.x: upgrade to version 2.2.2.148 or later
  4. 4. For FXOS 2.3.x: upgrade to version 2.3.1.216 or later
  5. 5. For FXOS 2.4.x: upgrade to version 2.4.1.273 or later
  6. 6. For FXOS 2.6.x: upgrade to version 2.6.1.224 or later
  7. 7. For IOS/IOS XE/IOS XR/NX-OS: upgrade to a version beyond 8.4(3.115), 7.0(3)i7(9), 7.3(8)n1(1), or 3.2(3o)a as listed in Cisco security advisory
  8. 8. Verify UDLD is not enabled if not needed: use 'show udld' and 'no udld enable' to disable if active
Caveat Standard firmware upgrade risks apply - ensure backup and test in lab first; UDLD feature behavior remains unchanged by fix

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Fxos Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,130
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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-2021-34714 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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