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Adaptive Security ApplianceApplication · Cisco

CVE-2021-34790

MEDIUM · 5.3 CVSS v3.1 Published 2021-10-27
Fix available
A fix is available. Upgrade to 6.4.0.12 / 6.6.5 or later.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

Multiple vulnerabilities in the Application Level Gateway (ALG) for Network Address Translation (NAT) in Cisco ASA and FTD software allow an unauthenticated, remote attacker to bypass the ALG and establish unauthorized inbound connections to hosts located behind the NAT (publicly discussed as NAT Slipstreaming).

MitigationApply the relevant Cisco security updates for ASA and FTD software to patch the ALG vulnerabilities; verify NAT traversal functionality after patching.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Adaptive Security ApplianceApplication
Affected:< 9.8.4.40
Secure Firewall Threat DefenseApplication
Affected:< 6.4.0.12>= 6.5.0, < 6.6.5>= 6.7.0, < 6.7.0.2
Adaptive Security Appliance SoftwareOperating system
Affected:>= 9.12.0, < 9.12.4.29>= 9.13.0, < 9.14.2.15>= 9.15.0, < 9.15.1.15
Asa 5512 X FirmwareOperating system
Affected:= 009.008= 009.015
Asa 5505 FirmwareOperating system
Affected:= 009.008= 009.015
Asa 5515 X FirmwareOperating system
Affected:= 009.008= 009.015
Asa 5525 X FirmwareOperating system
Affected:= 009.008= 009.015
Asa 5545 X FirmwareOperating system
Affected:= 009.008= 009.015

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify product and version
    Log into the Cisco ASA or FTD device CLI and run 'show version' to display the running software version. Note the exact version number displayed in the output.
    Affected if The displayed version falls within any of the following ranges: ASA < 9.8.4.40; FTD < 6.4.0.12, >= 6.5.0 < 6.6.5, >= 6.7.0 < 6.7.0.2; ASA >= 9.12.0 < 9.12.4.29, >= 9.13.0 < 9.14.2.15, >= 9.15.0 < 9.15.1.15; or matches specific firmware versions 009.008 or 009.015 for ASA 5512X, 5505, 5515X, 5525X, o
  2. Verify NAT is configured
    Run 'show nat' or 'show running-config nat' from the CLI to list active NAT rules.
    Affected if Any NAT configuration exists (NAT rules are present), indicating the ALG is processing traffic.
  3. Confirm ALG inspection is active
    Run 'show service-policy' and look for ALG-related inspection configurations such as DNS, FTP, H323, HTTP, RTSP, or SIP inspection.
    Affected if ALG inspection is enabled for any protocol, making the device vulnerable to ALG bypass.
  4. Check if device handles external traffic
    Review the interface configuration with 'show interface' and verify whether any NAT rule maps external (public) IP traffic to internal (private) hosts.
    Affected if The device performs NAT for traffic originating from untrusted networks, exposing the ALG to potential exploitation.

If the device runs an affected ASA or FTD version AND has NAT or ALG inspection configured for external traffic, the environment is vulnerable to CVE-2021-34790.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 6.4.0.12 / 6.6.5 / 6.7.0.2 or later
Fixed in 6.4.0.126.6.56.7.0.2
Interim mitigation

Apply the relevant Cisco security updates for ASA and FTD software to patch the ALG vulnerabilities; verify NAT traversal functionality after patching.

Recommended fix High confidence

Upgrade to ASA 9.8.4.40+ / 9.12.4.29+ / 9.14.2.15+ / 9.15.1.15+ or FTD 6.4.0.12+ / 6.6.5+ / 6.7.0.2+ depending on your release train

  1. 1. Identify the exact Cisco ASA or FTD version currently running using 'show version' command
  2. 2. Determine which release train your device is on (e.g., 9.8.x, 9.12.x, 9.13.x, 9.14.x, 9.15.x for ASA; or 6.4.x, 6.5.x, 6.6.x, 6.7.x for FTD)
  3. 3. For ASA: upgrade to version 9.8.4.40 or later if on 9.8 train; 9.12.4.29 or later if on 9.12 train; 9.14.2.15 or later if on 9.13/9.14 train; 9.15.1.15 or later if on 9.15 train
  4. 4. For FTD: upgrade to version 6.4.0.12 or later if on 6.4 train; 6.6.5 or later if on 6.5/6.6 train; 6.7.0.2 or later if on 6.7 train
  5. 5. For ASA 5500-X series firmware: upgrade to version 9.8.4.40 or later which includes the fixed firmware
  6. 6. Download the appropriate software image from Cisco and verify hash before upgrade
  7. 7. Schedule maintenance window and backup current configuration
  8. 8. Upload new image and reload device using 'reload' command
Caveat Review Cisco release notes for your specific version upgrade path as some upgrades may require intermediate steps; ensure compatibility with existing VPN, ACL, and NAT configurations

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Adaptive Security Appliance Scoped from the published advisory
  • Consultation4.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,780
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-34790 in production — separate from our analysis above.

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