Skip to main content
Live Webinar with SANS (June 25)— Agentic CTI Automation for Fun & ProfitRegister Free
Mallory
Medium

ACL bypass in Cisco Secure Firewall ASA/FTD clustering rule replication

IdentifiersCVE-2026-20073CWE-703

A vulnerability in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated remote attacker to send traffic that should be denied through an affected device. The issue is caused by improper error handling when a device that is joining a cluster runs out of memory while replicating access control rules, resulting in an access-control enforcement failure that permits otherwise-blocked traffic to pass.

Share:
For your environment

Are you exposed to this one?

Mallory correlates every CVE against your assets, your vendors, and active adversary campaigns. Know which vulnerabilities matter for you, not just which ones are loud.

ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation allows bypass of configured access controls/ACL policy enforcement on the affected ASA/FTD device, enabling unauthorized network reachability into protected networks (i.e., traffic that should be denied is permitted).

Mitigation

If you can’t patch tonight, do this now.

No specific mitigations are provided in the supplied content beyond remediation. As a practical risk-reduction measure based on the described condition, avoid/limit cluster join operations under memory pressure and ensure adequate memory headroom during rule replication events until fixed software can be deployed.

Remediation

Patch, then assume compromise.

Apply Cisco-provided fixed software updates for Cisco Secure Firewall ASA and Cisco Secure Firewall FTD that address CVE-2026-20073 (per the relevant Cisco Security Advisory for the ACL bypass/DoS issue).
PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType
Cisco SystemsAdaptive Security Appliance Softwareoperating_system
Cisco SystemsFirepower Threat Defenseapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.
Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity1

Community discussion across Reddit, Mastodon, and other social sources.