CVE-2021-1251

Service interruption via unchecked LLDP header lengths

Published Apr 8, 2021 · Updated Nov 8, 2024

Memory exhaustion in Cisco Small Business RV Series Router Firmware allows attackers to force an affected router to reload via LLDP packets. The LLDP implementation fails to validate the length of certain packet header fields, so a crafted packet drives continuous memory consumption. Exploitation requires Layer 2 adjacency and LLDP enabled; exhausted memory eventually triggers a reload and interrupts service without reported data disclosure or modification.

CVSS severity7.4
High
EPSS probability0.43%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory exhaustion in Cisco Small Business RV Series Router Firmware allows attackers to force an affected router to reload via LLDP packets. The LLDP implementation fails to validate the length of certain packet header fields, so a crafted packet drives continuous memory consumption. Exploitation requires Layer 2 adjacency and LLDP enabled; exhausted memory eventually triggers a reload and interrupts service without reported data disclosure or modification.

The record

CVE
CVE-2021-1251
Published
Apr 8, 2021
Updated
Nov 8, 2024
Vendor
ClamAV
Product
Cisco Small Business RV Series Router Firmware
Classifications
CWE-401, CWE-119, T1499.001
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?

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  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

6.1NIST NVDAV:A/AC:L/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

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
CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
T1499.001OS Exhaustion Flood

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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