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Adaptive Security ApplianceApplication · Cisco

CVE-2020-3555

HIGH · 7.5 CVSS v3.1 Published 2020-10-21
Fix available
A fix is available. Upgrade to 6.3.0.6 / 6.4.0.10 or later.
See remediation →
84/100
Remediation priority · High
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 SIP inspection process of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a crash and reload of an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to a watchdog timeout and crash during the cleanup of threads that are associated with a SIP connection that is being deleted from the connection list. An attacker could exploit this vulnerability by sending a high rate of crafted SIP traffic through an affected device. A successful exploit could allow the attacker to cause a watchdog timeout and crash, resulting in a crash and reload of the affected device.

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

A vulnerability exists in the SIP inspection engine of Cisco ASA and FTD software where a watchdog timeout occurs during thread cleanup when a SIP connection is deleted from the connection list. An unauthenticated remote attacker can exploit this by sending high-rate crafted SIP traffic, triggering the flawed cleanup path and causing a device crash and reload.

MitigationApply available Cisco patches for CVE-2020-3555. If no patch is available, rate-limit SIP traffic traversing the affected device or block SIP at the perimeter if not required for business functions.

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 ApplianceApplication
Affected:< 9.6.4.43
Secure Firewall Threat DefenseApplication
Affected:<= 6.2.2>= 6.3.0, < 6.3.0.6>= 6.4.0, < 6.4.0.10>= 6.5.0, < 6.5.0.5= 6.6.0
Adaptive Security Appliance SoftwareOperating system
Affected:>= 9.7.0, < 9.8.4.24>= 9.9.0, < 9.9.2.80>= 9.10.0, < 9.10.1.43>= 9.12.0, < 9.12.4.2>= 9.13.0, < 9.13.1.13>= 9.14.0, < 9.14.1.19

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
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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. Identify the device model and software type
    Run 'show version' and look for 'Cisco Adaptive Security Appliance' or 'Firepower Threat Defense' in the output
    Affected if The device is a Cisco ASA or FTD appliance
  2. Determine the installed software version
    Run 'show version' and note the version number (for ASA: look for something like 9.x.x; for FTD: look for 6.x.x)
    Affected if The version falls outside the fixed version ranges: ASA < 9.6.4.43, or ASA 9.7.x to 9.14.x with version less than the respective fix (9.8.4.24, 9.9.2.80, 9.10.1.43, 9.12.4.2, 9.13.1.13, or 9.14.1.19); FTD <= 6.2.2, 6.3.0 to < 6.3.0.6, 6.4.0 to < 6.4.0.10, 6.5.0 to < 6.5.0.5, or exactly 6.6.0
  3. Verify if SIP inspection is enabled
    Run 'show running-config | include sip' or 'show service-policy | include sip' to check for SIP inspection configuration
    Affected if SIP inspection is enabled (policy-map with 'inspect sip' present in the configuration)
  4. Confirm SIP traffic can reach the device
    Review access-list or security zone configuration to determine if SIP traffic (port 5060/UDP or TCP) is permitted through the device
    Affected if SIP traffic is allowed to traverse the device (inbound or between interfaces) and the device has SIP inspection enabled on that traffic

The device is affected if it runs a vulnerable ASA or FTD version AND has SIP inspection enabled AND SIP traffic can pass through the device.

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
Upgrade available Upgrade to 6.3.0.6 / 6.4.0.10 / 6.5.0.5 or later
Fixed in 6.3.0.66.4.0.106.5.0.5
Interim mitigation

Apply available Cisco patches for CVE-2020-3555. If no patch is available, rate-limit SIP traffic traversing the affected device or block SIP at the perimeter if not required for business functions.

Fix this in Adaptive Security Appliance Scoped from the published advisory
  • Consultation4.0 h
  • Implementation2.0 h
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,600
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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-2020-3555 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