CVE-2021-34790: Cisco Adaptive Security Appliance

Medium severity, CVSS 5.3. EPSS: 1.1% chance of exploitation in the next 30 days.

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.

Affected products

• Cisco Adaptive Security Appliance: before 9.8.4.40 (fixed in 9.8.4.40)
• Cisco Adaptive Security Appliance Software: from 9.12.0, before 9.12.4.29 (fixed in 9.12.4.29); from 9.13.0, before 9.14.2.15 (fixed in 9.14.2.15); from 9.15.0, before 9.15.1.15 (fixed in 9.15.1.15)
• Cisco ASA 5505 Firmware: version 009.008 only; version 009.015 only
• Cisco ASA 5512-X Firmware: version 009.008 only; version 009.015 only
• Cisco ASA 5515-X Firmware: version 009.008 only; version 009.015 only
• Cisco ASA 5525-X Firmware: version 009.008 only; version 009.015 only
• Cisco ASA 5545-X Firmware: version 009.008 only; version 009.015 only
• Cisco ASA 5555-X Firmware: version 009.008 only; version 009.015 only
• Cisco ASA 5580 Firmware: version 009.008 only; version 009.015 only
• Cisco ASA 5585-X Firmware: version 009.008 only; version 009.015 only
• Cisco Secure Firewall Threat Defense: before 6.4.0.12 (fixed in 6.4.0.12); from 6.5.0, before 6.6.5 (fixed in 6.6.5); from 6.7.0, before 6.7.0.2 (fixed in 6.7.0.2)

Published 2021-10-27. Last modified 2026-08-11.