CVE-2021-34714

Device reload via malformed UDLD packets

Published Sep 23, 2021 · Updated Nov 7, 2024

Improper input validation in Cisco IOS UDLD allows unauthenticated physically proximate attackers to reload affected devices. The UDLD packet handler fails to validate crafted protocol fields before processing packets received from a directly connected peer. UDLD is disabled by default, and exploitation requires full control of that peer; success reboots the device and interrupts service.

CVSS severity7.4
High
EPSS probability0.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Cisco IOS UDLD allows unauthenticated physically proximate attackers to reload affected devices. The UDLD packet handler fails to validate crafted protocol fields before processing packets received from a directly connected peer. UDLD is disabled by default, and exploitation requires full control of that peer; success reboots the device and interrupts service.

The record

CVE
CVE-2021-34714
Published
Sep 23, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco IOS
Classifications
CWE-20, T1499.004
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 23, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 7, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=n/a

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco IOSversion=n/a

Published CVSS scores

5.7NIST NVDAV:A/AC:M/Au:N/C:N/I:N/A:C
7.4Cisco Systems, Inc.CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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