CVE-2026-20019 in Snort
Summary
by MITRE • 10/22/2026
Multiple Cisco products are affected by a vulnerability in the Snort 3 NetFlow Detection Engine that could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to restart, resulting in an interruption of packet inspection.
This vulnerability is due to incomplete error checking when Snort 3 parses UDP Netflow Protocol packets. An attacker could exploit this vulnerability by sending a single crafted Netflow packet through an established connection to be parsed by Snort 3. A successful exploit could allow the attacker to cause the Snort 3 Detection Engine to restart unexpectedly, resulting in a DoS condition.
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Analysis
by VulDB Data Team • 10/22/2026
The Cisco Security Products are impacted by a critical vulnerability within the Snort 3 NetFlow Detection Engine that permits an unauthenticated remote attacker to trigger a denial of service against the detection infrastructure. This flaw stems from incomplete error checking during the parsing process for UDP Netflow Protocol packets, which allows malformed or crafted input to bypass standard validation routines. The core technical deficiency lies in how the engine handles specific packet structures without verifying their integrity before processing them further into the detection logic. When a single specially constructed NetFlow packet is transmitted through an established connection and reaches the Snort 3 parser, it triggers an internal error condition that forces the Detection Engine to restart unexpectedly. This behavior indicates a lack of robust exception handling or boundary checks within the code responsible for interpreting network flow data streams.
The operational impact of this vulnerability is significant as it directly compromises the availability of intrusion detection capabilities. By causing the Snort 3 Detection Engine to crash and restart, an attacker can effectively create a denial of service condition that interrupts packet inspection services. During the period when the engine is restarting or recovering from the fault, network traffic passes through without being analyzed by the security rulesets configured in Snort. This gap creates a window of opportunity where malicious activity may go undetected and unblocked, potentially allowing further exploitation attempts to succeed while the defense mechanism is temporarily disabled. The ability to trigger this restart with just one packet makes it particularly dangerous as it requires minimal effort from the attacker and can be executed remotely without any prior authentication credentials.
From a classification perspective, this vulnerability aligns closely with CWE-20 Improper Input Validation, specifically regarding the failure to validate data structures before processing them within a security-critical component. The mechanism of sending crafted network packets to trigger a crash is characteristic of denial-of-service attacks categorized under MITRE ATT&CK technique T1498 Network Denial of Service. Furthermore, because it involves manipulating protocol-specific parsing logic in an intrusion detection system, it also relates to CWE-755 Improper Handling of Exceptional Conditions and CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization if the restart process introduces race conditions during recovery. Understanding these mappings helps in prioritizing remediation efforts based on established industry standards for vulnerability management.
Mitigation strategies should focus primarily on applying vendor-provided patches that address the incomplete error checking within the Snort 3 NetFlow Detection Engine codebase. Organizations running affected Cisco products must ensure their intrusion detection systems are updated to versions where this parsing flaw has been corrected with proper input validation and exception handling mechanisms. In scenarios where immediate patching is not feasible, network segmentation can be employed to restrict access to the management interfaces of these devices or to limit exposure to untrusted networks that might send malicious NetFlow data. Additionally, enabling logging for engine restarts allows security teams to monitor for signs of exploitation attempts and respond quickly to potential denial-of-service events caused by this vulnerability.