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4.7Medium

Cisco Adaptive Security Appliance

CVE-2021-34791

Multiple vulnerabilities in the Application Level Gateway (ALG) for the Network Address Translation (NAT) feature of Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to bypass the ALG and open unauthorized connections with a host located behind the ALG. For more information about these vulnerabilities, see the Details section of this advisory. Note: These vulnerabilities have been publicly discussed as NAT Slipstreaming.

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, but only after tricking someone into an action such as opening a file or a link.

What to do

  1. 1Check whether your company or your suppliers run Cisco Adaptive Security Appliance, and which version. The affected versions are listed further down this page.
  2. 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

Check if you’re exposedBook a call

Scoring

CVSS
4.7 (v3.1)
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
Weakness
CWE-358
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- 6.4.0.12, 6.5.0 - 6.6.5, 6.7.0 - 6.7.0.2
  • Cisco Adaptive Security Appliance Software9.12.0 - 9.12.4.18, 9.13.0 - 9.14.2.15, 9.15.0 - 9.15.1.15
  • Cisco Asa 5512-X Firmware009.008, 009.015
  • Cisco Asa 5512-Xall versions
  • Cisco Asa 5505 Firmware009.008, 009.015
  • Cisco Asa 5505all versions
  • Cisco Asa 5515-X Firmware009.008, 009.015
  • Cisco Asa 5515-Xall versions
  • Cisco Asa 5525-X Firmware009.008, 009.015
  • Cisco Asa 5525-Xall versions
  • Cisco Asa 5545-X Firmware009.008, 009.015

As listed in the NVD configuration data. Not a statement about your estate.

References