How severe is CVE-2021-34791?

CVE-2021-34791 has a CVSS 3.x base score of 4.7, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2021-34791 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (62nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-34791?

CVE-2021-34791 primarily affects Cisco Adaptive Security Appliance. In total, 19 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-34791?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-34791 published?

CVE-2021-34791 was published on 2021-10-27 and last updated on 2026-06-17.

CVE-2021-34791

CVE-2021-34791 is a medium-severity vulnerability in Cisco Adaptive Security Appliance with a CVSS 3.x base score of 4.7. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: Medium (CVSS 3.x base score 4.7)
CVSS v2: 5.0
EPSS exploit prediction: 1% (62nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Cisco Adaptive Security Appliance
Published: 2021-10-27
Last modified: 2026-06-17

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.

Frequently asked questions

What is 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.
How severe is CVE-2021-34791?: CVE-2021-34791 has a CVSS 3.x base score of 4.7, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2021-34791 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (62nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-34791?: CVE-2021-34791 primarily affects Cisco Adaptive Security Appliance. In total, 19 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-34791?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-34791 published?: CVE-2021-34791 was published on 2021-10-27 and last updated on 2026-06-17.

References

https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-natalg-bypass-cpKGqkng

Affected products (19)

cpe:2.3:a:cisco:adaptive_security_appliance:*:*:*:*:*:*:*:*
cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5512-x_firmware:009.008:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5512-x_firmware:009.015:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5505_firmware:009.008:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5505_firmware:009.015:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5515-x_firmware:009.008:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5515-x_firmware:009.015:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5525-x_firmware:009.008:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5525-x_firmware:009.015:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5545-x_firmware:009.008:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5545-x_firmware:009.015:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5555-x_firmware:009.008:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5555-x_firmware:009.015:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5580_firmware:009.008:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5580_firmware:009.015:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5585-x_firmware:009.008:*:*:*:*:*:*:*
cpe:2.3:o:cisco:asa_5585-x_firmware:009.015:*:*:*:*:*:*:*

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