CVE-2021-40117Network attack vector

Unauthenticated device reload via crafted SSL/TLS packet

Published Oct 27, 2021 · Updated Nov 7, 2024

Denial of service in Cisco Adaptive Security Appliance Software allows remote attackers to reload affected devices via crafted SSL/TLS packets. The SSL/TLS message handler mishandles incoming packets under a CWE-119 memory-bounds condition, but Cisco does not disclose the exact buffer operation. Exposure requires a vulnerable release with AnyConnect IKEv2 client services, AnyConnect SSL VPN, or Clientless SSL VPN enabled; exploitation forces a device reload and service interruption.

CVSS severity8.6
High
EPSS probability1.53%
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 Adaptive Security Appliance Software allows remote attackers to reload affected devices via crafted SSL/TLS packets. The SSL/TLS message handler mishandles incoming packets under a CWE-119 memory-bounds condition, but Cisco does not disclose the exact buffer operation. Exposure requires a vulnerable release with AnyConnect IKEv2 client services, AnyConnect SSL VPN, or Clientless SSL VPN enabled; exploitation forces a device reload and service interruption.

The record

CVE
CVE-2021-40117
Published
Oct 27, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco Adaptive Security Appliance (ASA) Software
Classifications
CWE-400, CWE-119, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 27, 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 Adaptive Security Appliance (ASA) Softwareversion=n/a

Published CVSS scores

7.8NIST National Vulnerability DatabaseAV:N/AC:L/Au:N/C:N/I:N/A:C
7.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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

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-400Uncontrolled Resource Consumption
CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
T1499Endpoint Denial of Service

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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