CVE-2021-34791

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in, but needs a user to act. Limited direct impact.

Exploit odds

1.1% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-10-27 19:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-08-11 19:37 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 1.1% in the next 30 days (EPSS).
• Severity: 4.7 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-10-27 19:15 UTC

Last modified

2026-08-11 19:37 UTC

Exploit probability

1.1% · EPSS, next 30 days

Weakness

CWE-358

Record status

Modified

Affected

• Cisco Adaptive Security Appliance < 9.8.4.40
• Cisco Secure Firewall Threat Defense < 6.4.0.12
• Cisco Secure Firewall Threat Defense < 6.6.5
• Cisco Secure Firewall Threat Defense < 6.7.0.2
• Cisco Adaptive Security Appliance Software < 9.12.4.18
• Cisco Adaptive Security Appliance Software < 9.14.2.15
• Cisco Adaptive Security Appliance Software < 9.15.1.15
• Cisco Asa 5512-x Firmware 009.008

Attack profile CVSS 3.1 · 4.7

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

Required

Scope

Changed

Confidentiality

None

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-34791.md and follow it. Check whether this project is affected by CVE-2021-34791. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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