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Adaptive Security ApplianceApplication · Cisco

CVE-2021-34793

HIGH · 8.6 CVSS v3.1 Published 2021-10-27
Fix available
A fix is available. Upgrade to 6.4.0.13 / 6.6.5 or later.
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 TCP Normalizer of Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software operating in transparent mode could allow an unauthenticated, remote attacker to poison MAC address tables, resulting in a denial of service (DoS) vulnerability. This vulnerability is due to incorrect handling of certain TCP segments when the affected device is operating in transparent mode. An attacker could exploit this vulnerability by sending a crafted TCP segment through an affected device. A successful exploit could allow the attacker to poison the MAC address tables in adjacent devices, resulting in network disruption.

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 in the TCP Normalizer of Cisco ASA and FTD Software allows an unauthenticated remote attacker to poison MAC address tables by sending crafted TCP segments through affected devices operating in transparent mode, causing denial of service.

MitigationUpgrade Cisco ASA/FTD software to a patched version, or if upgrading is not feasible, consider migrating from transparent mode to routed mode or implement network segmentation to isolate affected devices.

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:< 9.8.4.40
Secure Firewall Threat DefenseApplication
Affected:< 6.4.0.13>= 6.5.0, < 6.6.5>= 6.7.0, < 6.7.0.3
Adaptive Security Appliance SoftwareOperating system
Affected:>= 9.9.0, < 9.12.4.29>= 9.13.0, < 9.14.3.9>= 9.15.0, < 9.15.1.17>= 9.16.0, < 9.16.2.3
Asa 5512 X FirmwareOperating system
Affected:= 009.008\(004.025\)
Asa 5505 FirmwareOperating system
Affected:= 009.008\(004.025\)
Asa 5515 X FirmwareOperating system
Affected:= 009.008\(004.025\)
Asa 5525 X FirmwareOperating system
Affected:= 009.008\(004.025\)
Asa 5545 X FirmwareOperating system
Affected:= 009.008\(004.025\)

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 is running in transparent mode
    Use the command to display the firewall mode configuration (typically 'show run firewall' or 'show mode'). Transparent mode is required for this vulnerability to be exploitable.
    Affected if The device is configured in transparent (bridge) mode rather than routed mode. Devices in routed mode are not affected by this CVE.
  2. Identify the Cisco ASA software version
    Run the command to display the running software version (typically 'show version' or 'show version | include Version'). Note the full version string including the maintenance release number.
    Affected if The installed version falls within any of these affected ranges: < 9.8.4.40; >= 9.9.0 and < 9.12.4.29; >= 9.13.0 and < 9.14.3.9; >= 9.15.0 and < 9.15.1.17; >= 9.16.0 and < 9.16.2.3
  3. Identify the Cisco FTD software version
    Run the command to display the FTD software version (typically 'show version' or 'systemtuuid'). Note the full version number.
    Affected if The installed version falls within any of these affected ranges: < 6.4.0.13; >= 6.5.0 and < 6.6.5; >= 6.7.0 and < 6.7.0.3
  4. Check specific ASA appliance firmware versions
    For ASA 5512-X, 5505, 5515-X, 5525-X, or 5545-X appliances, run the command to display the firmware version. Compare the firmware build number against 009.008(004.025).
    Affected if The firmware version equals exactly 009.008(004.025) on any of these specific ASA models

The device is vulnerable if it runs in transparent mode AND the installed software version or firmware build matches any of the affected version ranges listed for Cisco ASA or FTD.

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
Upgrade available Upgrade to 6.4.0.13 / 6.6.5 / 6.7.0.3 or later
Fixed in 6.4.0.136.6.56.7.0.3
Interim mitigation

Upgrade Cisco ASA/FTD software to a patched version, or if upgrading is not feasible, consider migrating from transparent mode to routed mode or implement network segmentation to isolate affected devices.

Recommended fix High confidence

Upgrade to Cisco ASA/FTD fixed releases: ASA 9.8.4.40+, 9.12.4.29+, 9.14.3.9+, 9.15.1.17+, or 9.16.2.3+; FTD 6.4.0.13+, 6.6.5+, or 6.7.0.3+

  1. 1. Identify the current Cisco ASA or FTD software version by running 'show version' on the device
  2. 2. Determine which software train (9.x, etc.) is currently in use
  3. 3. For ASA versions < 9.8.4.40: upgrade to 9.8.4.40 or later
  4. 4. For ASA versions >= 9.9.0 and < 9.12.4.29: upgrade to 9.12.4.29 or later
  5. 5. For ASA versions >= 9.13.0 and < 9.14.3.9: upgrade to 9.14.3.9 or later
  6. 6. For ASA versions >= 9.15.0 and < 9.15.1.17: upgrade to 9.15.1.17 or later
  7. 7. For ASA versions >= 9.16.0 and < 9.16.2.3: upgrade to 9.16.2.3 or later
  8. 8. For FTD versions < 6.4.0.13: upgrade to 6.4.0.13 or later
Caveat Review Cisco release notes for upgrade considerations; some upgrades may require intermediate steps depending on current version; ensure compatibility with any vpn, ACL, or policy configurations

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

Fix this in Adaptive Security Appliance Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2021-34793 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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