CVE-2021-1309

Code execution or reload via unchecked LLDP lengths

Published Apr 8, 2021 · Updated Nov 8, 2024

Improper length validation in Cisco Small Business RV Series Router Firmware allows attackers to execute code or reload affected routers. The LLDP implementation fails to validate certain packet-header length fields before processing a malicious LLDP packet. Exploitation requires Layer 2 adjacency in the same broadcast domain and can run arbitrary code or force an unexpected reboot.

CVSS severity8.8
High
EPSS probability0.52%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper length validation in Cisco Small Business RV Series Router Firmware allows attackers to execute code or reload affected routers. The LLDP implementation fails to validate certain packet-header length fields before processing a malicious LLDP packet. Exploitation requires Layer 2 adjacency in the same broadcast domain and can run arbitrary code or force an unexpected reboot.

The record

CVE
CVE-2021-1309
Published
Apr 8, 2021
Updated
Nov 8, 2024
Vendor
ClamAV
Product
Cisco Small Business RV Series Router Firmware
Classifications
CWE-401, T1210
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 8, 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 RV Series Router Firmwareversion=n/a

Published CVSS scores

7.4Cisco Systems, Inc. CNACVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
8.3NIST National Vulnerability DatabaseAV:A/AC:L/Au:N/C:C/I:C/A:C
8.8NIST National Vulnerability DatabaseCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
8.8Cisco Security AdvisoryCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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-401Missing Release of Memory after Effective Lifetime
T1210Exploitation of Remote Services

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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