dbcve.org
Double FreeWeakness · CWE-415

CVE-2025-20134

HIGH · 8.6 CVSS v3.1 Published 2025-08-14
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
95/100
Remediation priority · Urgent
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 certificate processing of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to improper parsing of SSL/TLS certificates. An attacker could exploit this vulnerability by sending crafted DNS packets that match a static Network Address Translation (NAT) rule with DNS inspection enabled through an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.

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 · moderate confidence

This is a denial-of-service vulnerability in Cisco ASA and FTD firewall software caused by improper SSL/TLS certificate parsing. An unauthenticated remote attacker can trigger device reload by sending crafted DNS packets that match a static NAT rule with DNS inspection enabled.

MitigationApply the Cisco security patch when available. Until then, consider disabling DNS inspection if not operationally critical, or implement additional filtering on upstream networks to drop malformed DNS packets before they reach the firewall.

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

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
Changed
Confidentiality
None
Integrity
None
Availability
High

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

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. Confirm device model and type
    Run 'show version' or 'show module' to identify if the device is Cisco ASA or Firepower Threat Defense (FTD)
    Affected if Device is not Cisco ASA or FTD - this CVE does not apply
  2. Identify static NAT rules
    Run 'show nat' or 'show running-config nat' to list configured NAT rules. Look for static NAT entries using the 'static' command
    Affected if No static NAT rules are configured - the device may not be exploitable
  3. Check if DNS inspection is enabled
    Run 'show service-policy inspect dns' or examine the running configuration for 'inspect dns' under the policy-map. Also check global inspection settings with 'show running-config | include inspect dns'
    Affected if DNS inspection is not enabled globally or on any traffic policy - the attack vector is not present
  4. Verify DNS inspection is applied to traffic
    Check if the DNS inspection policy is attached to an interface or global policy using 'show service-policy' or review the policy-map configuration
    Affected if DNS inspection exists in config but is not actively applied to traffic - risk is reduced
  5. Compare installed version to affected range
    Run 'show version' to obtain the ASA or FTD software version. Compare against the Cisco vulnerability advisory for CVE-2025-20134 to determine if your version falls within affected releases
    Affected if Running version is newer than the fixed release listed in Cisco advisory - device may not be affected

A device is affected if it is Cisco ASA or FTD with both a static NAT rule configured AND DNS inspection actively enabled, running an affected software version, as the attacker needs both conditions to send crafted DNS packets that trigger the vulnerability.

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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the Cisco security patch when available. Until then, consider disabling DNS inspection if not operationally critical, or implement additional filtering on upstream networks to drop malformed DNS packets before they reach the firewall.

Recommended fix Moderate confidence

Refer to Cisco advisory for your specific ASA or FTD version - Cisco will specify the fixed release (e.g., 9.x or 7.x train depending on your current version)

  1. Check the Cisco Security Advisory (cisco-sa) for CVE-2025-20134 on sec.cloudapps.cisco.com or cisco.com for the exact list of affected versions
  2. Identify your current Cisco ASA or FTD software version using 'show version' command
  3. Download and install the fixed software release specified in the Cisco advisory for your product model
  4. After upgrade, verify the device reloads normally and DNS inspection functions correctly
  5. Document the upgrade in change management and verify NAT rules with DNS inspection are working as expected
Caveat Review Cisco release notes for your target version for any configuration or feature changes before upgrading; test in staging environment first

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,580
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Scan for this in your stack

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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-2025-20134 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
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  • No spam, self-promotion, credentials, or personal data