Cisco Adaptive Security Appliance
CVE-2021-34793
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.
What this means for your business
- It affects Cisco Adaptive Security Appliance. It matters if your company, or a supplier that handles your data, runs it.
- An attacker can use it remotely, over a network, without a login, and without anyone at your company clicking anything.
- FIRST's prediction model gives it a 0.7% chance of attack attempts being seen in the next 30 days, ranking above 50% of all known flaws.
What to do
- 1Check whether your company or your suppliers run Cisco Adaptive Security Appliance, and which version. The affected versions are listed further down this page.
- 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.
Not sure if your company is exposed?
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Scoring
- CVSS
- 8.6 (v3.1)
- Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H- Weakness
- CWE-924
- Assigned by
- psirt@cisco.com
Dates
- Published
- 2021-10-27
- Last modified
- 2026-08-11
- Sources
- NVD
Affected products
- Cisco Adaptive Security Appliance- 9.8.4.40
- Cisco Secure Firewall Threat Defense- 6.4.0.13, 6.5.0 - 6.6.5, 6.7.0 - 6.7.0.3
- Cisco Adaptive Security Appliance Software9.9.0 - 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
- Cisco Asa 5512-X Firmware009.008\(004.025\)
- Cisco Asa 5512-Xall versions
- Cisco Asa 5505 Firmware009.008\(004.025\)
- Cisco Asa 5505all versions
- Cisco Asa 5515-X Firmware009.008\(004.025\)
- Cisco Asa 5515-Xall versions
- Cisco Asa 5525-X Firmware009.008\(004.025\)
- Cisco Asa 5525-Xall versions
- Cisco Asa 5545-X Firmware009.008\(004.025\)
As listed in the NVD configuration data. Not a statement about your estate.