CVE-2024-20526Network attack vector

SSH denial of service via session resource exhaustion

Published Oct 23, 2024 · Updated Oct 23, 2024

Resource exhaustion in Cisco ASA Software's SSH server allows remote attackers to deny new SSH connections with crafted messages. A logic error during SSH session establishment lets crafted SSH messages consume available SSH server resources until the five-connection limit is exceeded. Exposure requires SSH to be enabled and, for 9.18.4.40 or 9.20.3, the proprietary ASA SSH stack; existing sessions and user traffic continue, while restoring new SSH access requires a manual reboot.

CVSS severity5.3
Medium
EPSS probability0.49%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Cisco ASA Software's SSH server allows remote attackers to deny new SSH connections with crafted messages. A logic error during SSH session establishment lets crafted SSH messages consume available SSH server resources until the five-connection limit is exceeded. Exposure requires SSH to be enabled and, for 9.18.4.40 or 9.20.3, the proprietary ASA SSH stack; existing sessions and user traffic continue, while restoring new SSH access requires a manual reboot.

The record

CVE
CVE-2024-20526
Published
Oct 23, 2024
Updated
Oct 23, 2024
Vendor
ClamAV
Product
Cisco Adaptive Security Appliance (ASA) Software
Classifications
CWE-400, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 23, 2024CVE publishedPublication date reported by the CVE source.
  2. Oct 23, 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=9.16.4.67
  2. Affected versionversion=9.16.4.70
  3. Affected versionversion=9.18.4.40
  4. Affected versionversion=9.20.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco Adaptive Security Appliance (ASA) Softwareversion=9.16.4.67; version=9.16.4.70; version=9.18.4.40; version=9.20.3

Published CVSS scores

5.3CiscoCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/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
T1499.003Application 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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