Denial of Service Vulnerability in Cisco Secure Firewall ASA and FTD

Catalog analysis: CISA added this entry on October 29, 2026. The entry reflects catalog information retrieved on October 30, 2026, not a snapshot archived on the inclusion date. This site’s publication date is shown separately. Check current vendor guidance before acting.

What the vulnerability is

CVE-2026-76418 is an unchecked return value to NULL pointer dereference vulnerability (CWE-690) affecting Cisco Secure Firewall ASA Software and Cisco Secure FTD Software. This flaw allows an unauthenticated, remote attacker to cause the affected device to reload unexpectedly. The primary impact is a denial of service (DoS) condition, disrupting network connectivity and security functions provided by the firewall.

Exposure and applicability

This vulnerability applies to organizations deploying Cisco Secure Firewall ASA or FTD software. Because the flaw can be triggered by an unauthenticated remote attacker, assets with internet-facing interfaces are at higher risk of exploitation. The ability to force a device reload remotely makes this a high-priority exposure for infrastructure owners who rely on these devices for perimeter defense and availability.

Remediation priorities

Our analysis suggests prioritizing remediation based on the asset’s role in the network architecture and its level of exposure:

1. Internet-Facing Edge Devices: Assets acting as the primary gateway should be prioritized first, as they are directly reachable by unauthenticated remote actors.
2. Internal Segmentation Firewalls: While less exposed than edge devices, these should be addressed to prevent lateral movement or internal DoS attacks.
3. Redundant Pairs: In high-availability configurations, patching one node at a time is necessary to maintain uptime while reducing the window of exposure.

Corrective action requires applying mitigations as specified in the Cisco Security Advisory (cisco-sa-asaftd-tunnel-dos-s6mgkb75).

How to validate remediation

To ensure that exposure has been reduced, defenders should move beyond simple version checks. We recommend the following validation steps:

• Configuration Audit: Verify that the specific software versions identified in the vendor advisory as fixed have been successfully deployed across all affected nodes.
• Vendor-Specified Validation: Follow any specific verification commands or logs recommended by Cisco to confirm the patch is active and functioning as intended.
• State Verification: Confirm that the device has successfully rebooted into the patched version and that security policies remain intact post-update.

Limits and open questions

While patching reduces the likelihood of this specific NULL pointer dereference, it does not eliminate all DoS risks inherent to network edge devices. It remains unknown whether this vulnerability is being utilized by known ransomware campaigns. Additionally, while CISA has set a deadline for federal agencies, non-federal organizations must determine their own urgency based on their specific risk profile and the criticality of the affected assets.

Source and editorial note

CVE-2026-76418: Cisco Secure Firewall ASA Software and Cisco Secure FTD Software Unchecked Return Value to NULL Pointer Dereference Vulnerability · Source date: October 29, 2026 · Retrieved October 30, 2026.

Material facts are tied to the cited primary source. Recommendations are independent defensive analysis unless attributed to the source. Confirm consequential decisions against current authoritative guidance.

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