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Adaptive Security Appliance SoftwareOperating system · Cisco

CVE-2024-20526

MEDIUM · 5.3 CVSS v3.1 Published 2024-10-23
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A vulnerability in the SSH server of Cisco Adaptive Security Appliance (ASA) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition for the SSH server of an affected device. This vulnerability is due to a logic error when an SSH session is established. An attacker could exploit this vulnerability by sending crafted SSH messages to an affected device. A successful exploit could allow the attacker to exhaust available SSH resources on the affected device so that new SSH connections to the device are denied, resulting in a DoS condition. Existing SSH connections to the device would continue to function normally. The device must be rebooted manually to recover. However, user traffic would not be impacted and could be managed using a remote application such as Cisco Adaptive Security Device Manager (ASDM).

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

This is a logic error vulnerability in the SSH server of Cisco ASA Software. When an unauthenticated remote attacker sends crafted SSH messages during session establishment, it exhausts available SSH resources on the device, preventing new SSH connections. Existing sessions continue normally, but new connections are denied until the device is manually rebooted.

MitigationApply the Cisco software update/patch when available. As a temporary measure, restrict SSH access to trusted management networks using access-lists to reduce exposure to unauthenticated attackers.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Adaptive Security Appliance SoftwareOperating system
Affected:= 9.16.4.67= 9.16.4.70= 9.18.4.40= 9.20.3

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the Cisco ASA software version
    Run the command 'show version' on the ASA CLI or retrieve the version via SNMP/management interface. Look for the software version number in the output.
    Affected if The installed version matches exactly 9.16.4.67, 9.16.4.70, 9.18.4.40, or 9.20.3
  2. Verify SSH server is enabled
    Run the command 'show ssh' on the ASA CLI to list active SSH sessions and confirm the SSH server is listening for connections.
    Affected if SSH server is enabled and the device is accepting SSH connections
  3. Check SSH access control configuration
    Run 'show running-config | include ssh' to review the SSH access-list configuration. Check if SSH is permitted from any external or untrusted networks versus only trusted management subnets.
    Affected if SSH is accessible from untrusted or management-bypass networks (0.0.0.0/0 or non-restricted ACLs)
  4. Monitor for SSH connection failures
    Run 'show ssh' repeatedly or review syslogs for indications that new SSH connections are being rejected while existing sessions remain active.
    Affected if New SSH connections are being denied but existing SSH sessions still work, indicating resource exhaustion

A user is affected if the ASA runs one of the exact affected versions (9.16.4.67, 9.16.4.70, 9.18.4.40, or 9.20.3) with SSH enabled and accessible, and they observe new SSH connections being rejected while existing sessions function normally.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the Cisco software update/patch when available. As a temporary measure, restrict SSH access to trusted management networks using access-lists to reduce exposure to unauthenticated attackers.

Fix this in Adaptive Security Appliance Software Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2024-20526 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data