CVE-2021-34790: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Application Level Gateway Bypass Vulnerabilities

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-10-27 · updated 2026-08-11
Weakness: CWE-358

Description

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 ASA Software: from 9.12.0 before 9.12.4.29; from 9.13.0 before 9.14.2.15; from 9.15.0 before 9.15.1.15 — fixed in 9.12.4.29, 9.14.2.15, 9.15.1.15
Cisco Asa 5505 Firmware: 009.008, 009.015
Cisco Asa 5512-X Firmware: 009.008, 009.015
Cisco Asa 5515-X Firmware: 009.008, 009.015
Cisco Asa 5525-X Firmware: 009.008, 009.015
Cisco Asa 5545-X Firmware: 009.008, 009.015
Cisco Asa 5555-X Firmware: 009.008, 009.015
Cisco Asa 5580 Firmware: 009.008, 009.015
Cisco Asa 5585-X Firmware: 009.008, 009.015
Cisco Firepower Threat Defense Software: before 6.4.0.12; from 6.5.0 before 6.6.5; from 6.7.0 before 6.7.0.2 — fixed in 6.4.0.12, 6.6.5, 6.7.0.2

How to fix

Upgrade to a fixed version: Cisco Adaptive Security Appliance 9.8.4.40; Cisco ASA Software 9.12.4.29, 9.14.2.15, 9.15.1.15; Cisco Firepower Threat Defense Software 6.4.0.12, 6.6.5, 6.7.0.2. Check the vendor advisory for mitigations.

References

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