CVE-2023-20042Network attack vector

VPN service interruption via SSL session-handler leak

Published Nov 1, 2023 · Updated Aug 2, 2024

Denial of service in Cisco ASA and FTD AnyConnect SSL VPN allows remote attackers to block new VPN sessions with crafted TLS traffic. The SSL/TLS session-handling path fails to release a session handler under specific conditions, so repeated crafted traffic leaks handlers until the pool is exhausted. Exposure requires AnyConnect SSL/TLS VPN to be configured; successful exploitation prevents new sessions but does not disclose or modify data.

CVSS severity6.8
Medium
EPSS probability0.68%
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 ASA and FTD AnyConnect SSL VPN allows remote attackers to block new VPN sessions with crafted TLS traffic. The SSL/TLS session-handling path fails to release a session handler under specific conditions, so repeated crafted traffic leaks handlers until the pool is exhausted. Exposure requires AnyConnect SSL/TLS VPN to be configured; successful exploitation prevents new sessions but does not disclose or modify data.

The record

CVE
CVE-2023-20042
Published
Nov 1, 2023
Updated
Aug 2, 2024
Vendor
ClamAV
Product
Cisco Adaptive Security Appliance (ASA) Software
Classifications
CWE-404, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 1, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 2, 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=9.16.1
  2. Affected versionversion=9.16.1.28
  3. Affected versionversion=9.16.2
  4. Affected versionversion=9.16.2.11
  5. Affected versionversion=9.16.2.13
  6. Affected versionversion=9.16.2.14
  7. Affected versionversion=9.16.2.3
  8. Affected versionversion=9.16.2.7
  9. Affected versionversion=9.16.3
  10. Affected versionversion=9.16.3.14
  11. Affected versionversion=9.16.3.15
  12. Affected versionversion=9.16.3.19
  13. Affected versionversion=9.16.3.23
  14. Affected versionversion=9.16.3.3
  15. Affected versionversion=9.16.4
  16. Affected versionversion=9.16.4.9
  17. Affected versionversion=9.17.1
  18. Affected versionversion=9.17.1.10
  19. Affected versionversion=9.17.1.11
  20. Affected versionversion=9.17.1.13
  21. Affected versionversion=9.17.1.15
  22. Affected versionversion=9.17.1.20
  23. Affected versionversion=9.17.1.7
  24. Affected versionversion=9.17.1.9
  25. Affected versionversion=9.18.1
  26. Affected versionversion=9.18.1.3
  27. Affected versionversion=9.18.2
  28. Affected versionversion=9.18.2.5
  29. Affected versionversion=9.18.2.7
  30. Affected versionversion=9.19.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco Adaptive Security Appliance (ASA) Softwareversion=9.16.1; version=9.16.1.28; version=9.16.2; version=9.16.2.11; version=9.16.2.13; version=9.16.2.14; version=9.16.2.3; version=9.16.2.7; version=9.16.3; version=9.16.3.14; version=9.16.3.15; version=9.16.3.19; version=9.16.3.23; version=9.16.3.3; version=9.16.4; version=9.16.4.9; version=9.17.1; version=9.17.1.10; version=9.17.1.11; version=9.17.1.13; version=9.17.1.15; version=9.17.1.20; version=9.17.1.7; version=9.17.1.9; version=9.18.1; version=9.18.1.3; version=9.18.2; version=9.18.2.5; version=9.18.2.7; version=9.19.1
ClamAV · Cisco Firepower Threat Defenseversion=7.0.0; version=7.0.0.1; version=7.0.1; version=7.0.1.1; version=7.0.2; version=7.0.2.1; version=7.0.3; version=7.0.4; version=7.0.5; version=7.1.0; version=7.1.0.1; version=7.1.0.2; version=7.1.0.3; version=7.2.0; version=7.2.0.1; version=7.2.1; version=7.2.2; version=7.2.3; version=7.3.0; version=7.3.1; version=7.3.1.1

Published CVSS scores

6.8Cisco Systems, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
8.6NIST NVDCVSS:3.1/AV:N/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-404Improper Resource Shutdown or Release
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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