CVE-2021-34777

LLDP memory corruption via missing length checks

Published Oct 6, 2021 · Updated Nov 7, 2024

Memory corruption in Cisco Small Business 220 Series Smart Switches allows adjacent attackers to corrupt LLDP databases via crafted LLDP packets. Missing length validation while processing LLDP messages permits an out-of-bounds read of packet data into the internal LLDP database. Exploitation requires an unauthenticated attacker on the same Layer 2 broadcast domain and can corrupt switch state; Cisco reports no public exploitation.

CVSS severity4.3
Medium
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory corruption in Cisco Small Business 220 Series Smart Switches allows adjacent attackers to corrupt LLDP databases via crafted LLDP packets. Missing length validation while processing LLDP messages permits an out-of-bounds read of packet data into the internal LLDP database. Exploitation requires an unauthenticated attacker on the same Layer 2 broadcast domain and can corrupt switch state; Cisco reports no public exploitation.

The record

CVE
CVE-2021-34777
Published
Oct 6, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco Small Business 200 Series Smart Switches
Classifications
CWE-120, CWE-125, T1565
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 6, 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 Small Business 200 Series Smart Switchesversion=n/a

Published CVSS scores

4.3Cisco Systems, Inc.CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
2.9National Institute of Standards and TechnologyAV:A/AC:M/Au:N/C:N/I:P/A:N

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-120Classic Buffer Overflow
CWE-125Out-of-bounds Read
T1565Data Manipulation

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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