Cisco Snort 3 Flaws Enable DoS and Data Leaks

Two vulnerabilities in Cisco's Snort 3 detection engine create opportunities for unauthenticated attackers to either crash the inspection system or extract sensitive data flowing through monitored networks. The flaws affect multiple Cisco security products, and the company explicitly states no workarounds exist.

CVE-2026-20026 triggers denial of service through a use-after-free condition. CVE-2026-20027 enables information disclosure via an out-of-bounds read. Both stem from improper buffer handling in DCE/RPC protocol parsing.

What Is Snort 3?

Snort is Cisco's open-source intrusion detection and prevention system. Version 3 represents a complete architectural rewrite designed to improve performance and extensibility. Organizations deploy Snort to monitor network traffic for malicious activity, making it a critical security control in many environments.

When Snort fails, blind spots emerge. Traffic passes uninspected. Alerts stop firing. Security teams lose visibility into what's happening on their networks.

Technical Details

The vulnerabilities exist in how Snort 3 processes Distributed Computing Environment/Remote Procedure Call (DCE/RPC) traffic. This protocol underlies Microsoft's network services, including SMB file sharing and Active Directory operations.

CVE-2026-20026 (CVSS 5.8) creates a denial of service condition. When processing large volumes of crafted DCE/RPC requests, Snort's buffer handling logic fails to properly manage memory. The engine references memory it has already freed, triggering unexpected restarts and interrupting packet inspection.

CVE-2026-20027 (CVSS 5.3) results from an out-of-bounds read. Attackers can extract sensitive data flowing through the inspection engine—potentially including credentials, session tokens, or other confidential information in monitored traffic.

Exploitation requires sending a large volume of crafted DCE/RPC requests through an established connection that Snort monitors. An attacker positioned on the network can trigger either condition without authentication.

Affected Products

The following Cisco products are vulnerable:

• Firepower Threat Defense (FTD) - Versions 7.0 and 7.2
• Cisco IOS XE - Current versions until 26.1.1 (February 2026)
• Meraki MX Series - Models MX67 through MX600 and virtual variants
• Standalone Snort 3 - Versions prior to 3.9.6.0

Meraki appliances remain vulnerable until scheduled patches arrive in February 2026. Organizations relying on these devices for network security should factor this gap into their risk assessments.

Why This Matters

Network intrusion detection operates as a silent guardian—when it works. These vulnerabilities turn that guardian into either a blind sentry (when crashed) or a data leak (when exploited for information disclosure).

The denial of service impact is straightforward: attackers can disable network monitoring before launching their actual attack. The information disclosure risk is more nuanced. Snort processes network traffic in real time, meaning sensitive data passing through could be captured by attackers who can trigger CVE-2026-20027.

DCE/RPC traffic is common in Windows environments. The affected protocol carries authentication exchanges, file operations, and administrative commands. An attacker extracting data from this traffic stream gains insight into the target organization's operations and potentially credentials for further access.

Patches and Mitigations

Cisco's advisory is clear: update or accept the risk. No workarounds exist.

Available patches:

• Snort 3.9.6.0 for open-source deployments
• Hotfixes for FTD versions 7.0 and 7.2 via Cisco Software Center
• Cisco IOS XE updates in version 26.1.1 (February 2026)
• Meraki MX patches scheduled for February 2026

Organizations with exposure should prioritize the update. The PSIRT advisory reports no active exploitation, but that calculus changes once technical details circulate.

For environments where immediate patching isn't possible, consider whether affected devices can be placed behind additional network controls. This doesn't eliminate the vulnerability but may reduce attack surface until patches deploy.

Detection teams should monitor for unusual volumes of DCE/RPC traffic directed at network segments where Snort operates. Sudden spikes could indicate exploitation attempts.