CVE-2021-1624Network attack vector

Service interruption via rate-limited NAT traffic

Published Sep 23, 2021 · Updated Nov 7, 2024

Denial of service in Cisco IOS XE Software allows remote attackers to exhaust the QuantumFlow Processor via rate-limited NAT traffic. The Rate Limiting NAT feature mishandles large traffic volumes subject to configured max-entries limits, driving processor utilization to 100 percent. Exposure requires Rate Limiting NAT on a transit device; unauthenticated traffic through that device can interrupt service without changing data or configuration.

CVSS severity8.6
High
EPSS probability1.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Cisco IOS XE Software allows remote attackers to exhaust the QuantumFlow Processor via rate-limited NAT traffic. The Rate Limiting NAT feature mishandles large traffic volumes subject to configured max-entries limits, driving processor utilization to 100 percent. Exposure requires Rate Limiting NAT on a transit device; unauthenticated traffic through that device can interrupt service without changing data or configuration.

The record

CVE
CVE-2021-1624
Published
Sep 23, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco IOS XE Software
Classifications
CWE-399, T1498.001
Attack vector
network
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 vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco IOS XE Softwareversion=n/a

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
8.6CiscoCVSS:3.1/AV:N/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-399Resource Management Errors
T1498.001Network Denial of Service: Direct Network 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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