CVE-2021-1236
MediumCVSS 5.3Exploitation Probability (EPSS)
High risk80th percentile - higher than 80% of all known CVEs
Summary
A vulnerability in the Snort application detection engine of multiple Cisco products could allow an unauthenticated, remote attacker to bypass configured policies. The issue is due to a flaw in the detection algorithm. An attacker could send crafted packets through an affected system, potentially bypassing policies and delivering a malicious payload.
Risk Assessment
The risk is that an attacker can bypass security policies and deliver malware to the protected network.
Recommendation
It is recommended to upgrade to a patched version and follow vendor guidance.
Other vulnerabilities in Snort
See all- CVE-2016-1417High
The vulnerability in Snort 2.9.7.0-WIN32 related to an untrusted search path allows remote attackers to execute arbitrary code and conduct DLL hijacking attacks via a malicious tcapi.dll file located in the same folder as a processed pcap file.
- CVE-2026-20068Medium
Vulnerability in the Snort 3 detection engine in multiple Cisco products allows an unauthenticated, remote attacker to cause the engine to restart, interrupting packet inspection. It is due to incomplete error checking when parsing RPC data.
- CVE-2026-20067Medium
Multiple Cisco products are affected by a vulnerability in the Snort 3 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 parsing the Multicast DNS fields of the HTTP header. An attacker could exploit this vulnerability by sending crafted HTTP packets through an established connection to be parsed by Snort 3. A successful exploit could allow the attacker to cause a DoS condition when the Snort 3 Detection Engine unexpectedly restarts.
- CVE-2026-20066Medium
Multiple Cisco products are affected by a vulnerability in the Snort 3 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 an error in the JSTokenizer normalization logic when the HTTP inspection normalizes JavaScript. An attacker could exploit this vulnerability by sending crafted HTTP packets through an established connection that is parsed by Snort 3. A successful exploit could allow the attacker to cause a DoS condition when the Snort 3 Detection Engine restarts unexpectedly. JSTokenizer is not enabled by default.
- CVE-2026-20058Medium
Multiple Cisco products are affected by vulnerabilities in the Snort 3 VBA feature that could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to crash. These vulnerabilities are due to improper error checking when decompressing VBA data. An attacker could exploit these vulnerabilities by sending crafted VBA data to the Snort 3 Detection Engine on the targeted device. A successful exploit could allow the attacker to cause the Snort 3 Detection Engine to unexpectedly restart, causing a DoS condition.
- CVE-2026-20005Medium
Multiple Cisco products are affected by a vulnerability in the Snort 3 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 parsing of the SSL handshake ingress packets. An attacker could exploit this vulnerability by sending crafted SSL handshake packets. A successful exploit could allow the attacker to cause a denial of service (DoS) condition when the Snort 3 Detection Engine restarts unexpectedly.
- CVE-2025-20359Medium
A vulnerability in the Snort 3 HTTP Decoder due to a buffer handling error when parsing MIME fields of the HTTP header can result in a buffer under-read. An unauthenticated remote attacker can send crafted HTTP packets to cause information disclosure or a crash of the Snort 3 Detection Engine.
- CVE-2022-20685High
A vulnerability in the Modbus preprocessor of the Snort detection engine could allow an unauthenticated, remote attacker to cause a denial of service (DoS). The issue is due to an integer overflow while processing Modbus traffic. Exploitation involves sending crafted Modbus traffic.
- CVE-2023-20267Medium
A vulnerability in the IP geolocation rules of Snort 3 could allow an unauthenticated, remote attacker to bypass IP address restrictions. This is due to improper parsing of the configuration for IP geolocation rules.
- CVE-2023-20246Medium
Multiple Cisco products are affected by a vulnerability in Snort access control policies that could allow an unauthenticated, remote attacker to bypass configured policies. This is due to a logic error when access control policies are populated. An attacker could exploit this by establishing a connection, potentially bypassing access control rules.
Original NVD description (English source)
Multiple Cisco products are affected by a vulnerability in the Snort application detection engine that could allow an unauthenticated, remote attacker to bypass the configured policies on an affected system. The vulnerability is due to a flaw in the detection algorithm. An attacker could exploit this vulnerability by sending crafted packets that would flow through an affected system. A successful exploit could allow the attacker to bypass the configured policies and deliver a malicious payload to the protected network.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

