Two critical vulnerabilities in Cisco’s Snort 3 detection engine have been disclosed, potentially compromising network security for numerous organizations. These flaws, identified as CVE-2026-20026 and CVE-2026-20027, allow remote attackers to either disrupt packet inspection services or leak sensitive data from affected systems. The discoveries highlight ongoing challenges in securing sophisticated network security tools against evolving threats.
The vulnerabilities specifically impact Cisco Secure Firewall Threat Defense (FTD) 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 at risk, as Snort 3 is enabled by default in these versions. The widespread deployment of Snort 3 means a significant attack surface exists for malicious actors.
Cisco Snort 3 Detection Engine Vulnerability Exposes Sensitive Data
The newly identified vulnerabilities in the Cisco Snort 3 detection engine stem from improper handling of Distributed Computing Environment and Remote Procedure Call (DCE/RPC) requests. Attackers can exploit these weaknesses without requiring any form of authentication, making them particularly dangerous for internet-facing network devices. The exploits involve sending specially crafted DCE/RPC requests through established network connections that are being monitored by Snort 3.
According to Cisco’s analysis, the flaws were found while examining the detection engine’s buffer handling mechanisms. CVE-2026-20026 is described as a use-after-free condition within buffer processing. This can lead to unexpected engine restarts and denial-of-service (DoS) conditions, effectively disabling the security device. The second vulnerability, CVE-2026-20027, is an out-of-bounds read flaw that allows attackers to extract sensitive data that is passing through the inspection engine.
Understanding the Technical Mechanism Behind the Flaws
The root cause of these vulnerabilities lies in the inadequate validation of DCE/RPC protocol parsing logic within Snort 3’s detection engine. When the system encounters a large volume of DCE/RPC requests, the buffer management logic fails to correctly control memory boundaries. This lapse creates conditions where the engine might attempt to access memory that has already been deallocated or read beyond the allocated buffer space.
An attacker can trigger this vulnerability by sending a high volume of crafted DCE/RPC requests over an active network connection monitored by Snort 3. The engine’s imperfect response to this overload can result in the leakage of sensitive data from adjacent memory locations or a complete system crash, thereby halting all packet inspection activities. This impact can significantly blind security teams to ongoing threats within their networks.
The vulnerabilities present distinct but serious risks. CVE-2026-20026, with a medium CVSS score of 5.8, focuses on disrupting network services, while CVE-2026-20027, with a CVSS score of 5.3, pertains to information disclosure. Cisco has addressed these issues by releasing updated versions, including Snort 3.9.6.0 and various hotfixes for its Secure FTD software. Organizations are strongly advised to implement these updates as a priority to mitigate the risks associated with these network security flaws.
Moving forward, network administrators should closely monitor Cisco’s security advisories for any further updates or patches. The ongoing patching and upgrading of network security infrastructure remain critical steps in defending against sophisticated cyber threats. The effectiveness of these measures will depend on the swift adoption of the provided fixes by affected organizations, ensuring the continued integrity and confidentiality of their network traffic.