CVE-2024-20431: Cisco Secure Firewall Auth Bypass Vulnerability

CVE-2024-20431 Overview

Cisco disclosed CVE-2024-20431, a geolocation access control bypass in Cisco Firepower Threat Defense (FTD) Software. The vulnerability lets an unauthenticated, remote attacker send traffic that circumvents geolocation-based access control policies. Improper assignment of geolocation data to network traffic causes the FTD engine to evaluate flows against the wrong region, allowing packets that should be blocked to reach protected assets. The flaw affects a wide range of FTD releases in the 7.0.x through 7.4.x branches.

Critical Impact
Attackers can route traffic to internal assets that administrators intended to block by country or region, weakening perimeter segmentation controls on Cisco FTD appliances.

Affected Products

Cisco Secure Firewall Threat Defense 7.0.0 through 7.0.6.1
Cisco Secure Firewall Threat Defense 7.1.0 through 7.2.5.2
Cisco Secure Firewall Threat Defense 7.3.0 through 7.4.1.1

Discovery Timeline

2024-10-23 - CVE-2024-20431 published to the National Vulnerability Database
2026-08-11 - Last updated in NVD database

Technical Details for CVE-2024-20431

Vulnerability Analysis

The vulnerability resides in the geolocation access control feature of Cisco FTD Software. FTD enriches inbound flows with geolocation metadata derived from source IP addresses, then evaluates that metadata against administrator-defined access control policies. When the metadata is assigned incorrectly, policy rules that reference a country or continent no longer match the actual traffic origin.

The result is a policy evaluation failure classified under [CWE-229] (Improper Handling of Values). Traffic that should have been denied for originating from a blocked geography instead traverses the firewall and reaches internal services. The scope is changed because a flaw in the geolocation subsystem alters authorization decisions enforced elsewhere in the policy stack.

Because the flaw sits in the data plane, no authentication or user interaction is required. Any attacker capable of sending traffic through an affected device may trigger the misclassification.

Root Cause

Cisco attributes the defect to improper assignment of geolocation data during flow classification. The FTD engine associates flows with country codes that do not correspond to the true source address, causing geolocation match criteria in access control rules to fail.

Attack Vector

Exploitation is straightforward: an attacker sends network traffic through an affected FTD device toward a protected resource governed by a geolocation-based access control policy. If the geolocation assignment is incorrect for that flow, the rule that would have blocked the traffic does not match, and the packets are forwarded. No credentials, exploit tooling, or malformed payloads are required. See the Cisco Security Advisory for the vendor's technical description.

Detection Methods for CVE-2024-20431

Indicators of Compromise

Connection events on FTD showing allowed traffic from source IP addresses that resolve to geographies explicitly denied by policy.
Access control rule hit counts that do not align with expected geolocation-based deny patterns.
Session logs on internal services showing successful requests from regions that should be blocked at the perimeter.

Detection Strategies

Cross-reference FTD connection event logs with an independent IP geolocation source to identify flows whose assigned country differs from the authoritative lookup.
Deploy compensating deny rules based on source IP address ranges or ASN and alert when those rules fire on traffic that geolocation rules should have already blocked.
Correlate firewall logs with server-side application logs to surface successful sessions originating from denied regions.

Monitoring Recommendations

Forward FTD connection and intrusion events to a centralized analytics platform for continuous geolocation policy validation.
Build dashboards that track allow-versus-deny ratios for each geolocation rule and alert on statistically anomalous drift.
Review Firepower Management Center audit logs for changes to geolocation feed updates or rule ordering that could mask exploitation.

How to Mitigate CVE-2024-20431

Immediate Actions Required

Inventory all Cisco FTD devices running versions in the 7.0.x, 7.1.x, 7.2.x, 7.3.x, and 7.4.x branches and identify those that enforce geolocation-based rules.
Apply the fixed software release identified in the Cisco Security Advisory.
Where patching cannot occur immediately, add explicit source-IP or ASN-based deny rules that duplicate the intent of geolocation rules for high-risk regions.

Patch Information

Cisco has published fixed software for Cisco Secure Firewall Threat Defense. Consult the vendor advisory for the specific patched release that maps to your deployed train, and follow standard FTD upgrade procedures through Firepower Management Center or the Cisco Defense Orchestrator.

Workarounds

Replace or augment geolocation-based deny rules with explicit IP-prefix or ASN-based deny lists sourced from a trusted feed.
Restrict exposed services behind additional authentication or VPN controls so that a bypassed geolocation rule does not directly expose the application.
Enable enhanced logging on any rule that references geolocation criteria to increase visibility into potential bypass attempts until the patch is deployed.

bash

# Configuration example
# See the Cisco Security Advisory for the fixed release that matches your deployment:
# https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-geoip-bypass-MB4zRDu