CVE-2021-34698Network attack vector

Service interruption via HTTPS connection memory exhaustion

Published Oct 6, 2021 · Updated Nov 7, 2024

Denial of service in affected Cisco Secure Web Appliance AsyncOS releases allows remote attackers to stop new connections over HTTPS. The proxy service fails to release memory while handling large numbers of HTTPS connections, allowing allocation to climb until accept handlers are disabled. No authentication or user interaction is required, and restoring normal proxy operation can require a device reload.

CVSS severity8.6
High
EPSS probability1.43%
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 affected Cisco Secure Web Appliance AsyncOS releases allows remote attackers to stop new connections over HTTPS. The proxy service fails to release memory while handling large numbers of HTTPS connections, allowing allocation to climb until accept handlers are disabled. No authentication or user interaction is required, and restoring normal proxy operation can require a device reload.

The record

CVE
CVE-2021-34698
Published
Oct 6, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco Secure Web Appliance
Classifications
CWE-401, T1499.002
Attack vector
network
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 vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco Secure Web Applianceversion=n/a

Published CVSS scores

7.8NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:C
8.6Cisco Systems, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-401Missing Release of Memory after Effective Lifetime
T1499.002Service 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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