Cisco Snort 3 Detection Engine Vulnerability Leaks Sensitive Data

Two critical vulnerabilities have been identified in Cisco’s Snort 3 detection engine, posing significant risks to network security infrastructure across multiple Cisco products.

These weaknesses stem from improper handling of Distributed Computing Environment and Remote Procedure Call (DCE/RPC) requests, allowing remote attackers to either disrupt packet inspection services or extract sensitive information from the system.

The vulnerabilities affect Cisco Secure Firewall Threat Defense software, open-source Snort 3, Cisco IOS XE software with Unified Threat Defense capabilities, and various Cisco Meraki appliances.

Organizations running Snort 3 on new installations of Cisco Secure FTD releases 7.0.0 and later are particularly vulnerable, as Snort 3 operates by default in these versions.

The attack surface remains extensive given the widespread deployment of Snort 3 across enterprise networks worldwide.

Attackers can launch these exploits without requiring any form of authentication, making them especially dangerous for internet-facing systems.

The vulnerabilities require sending specially crafted DCE/RPC requests through established network connections monitored by Snort 3.

Cisco analysts identified these flaws while examining the detection engine’s buffer handling mechanisms. The first vulnerability, CVE-2026-20026, involves a use-after-free condition in buffer processing that can trigger unexpected engine restarts and denial of service conditions.

The second vulnerability, CVE-2026-20027, results from an out-of-bounds read flaw that enables attackers to extract sensitive data flowing through the inspection engine.

Understanding the Technical Mechanism

The core issue originates from inadequate validation of DCE/RPC protocol parsing logic within Snort 3’s detection engine. When the system processes a large number of DCE/RPC requests, the buffer handling logic fails to properly manage memory boundaries.

This creates conditions where the engine either references memory it has previously freed or reads beyond allocated buffer boundaries.

An attacker exploiting this mechanism sends numerous DCE/RPC requests over an established connection, deliberately triggering the buffer mishandling.

The engine responds by either leaking sensitive data from adjacent memory regions or crashing entirely, interrupting all packet inspection operations.

Cisco has released fixed versions including Snort 3.9.6.0 and various hot fixes for Secure FTD software. Organizations should prioritize upgrades immediately to restore full protection against these network-layer threats.

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