CVE-2021-1236 in Integrated Services Router
Summary
by MITRE • 01/14/2021
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.
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Analysis
by VulDB Data Team • 02/14/2021
This vulnerability resides within Cisco's Snort application detection engine, a widely deployed network intrusion detection system that serves as a critical security control for network traffic monitoring and threat detection. The flaw represents a fundamental weakness in the detection algorithm that governs how the system processes and evaluates network packets against configured security policies. The vulnerability specifically affects multiple Cisco products that incorporate Snort as their core detection engine, creating a widespread impact across various network security appliances and solutions. The issue manifests as a bypass mechanism that allows unauthorized remote access to systems that should be protected by configured security policies, fundamentally undermining the integrity of network security controls.
The technical implementation of this vulnerability stems from a flaw in the detection algorithm that processes incoming network traffic. An attacker can exploit this weakness by crafting specially designed packets that are designed to evade the normal detection mechanisms. These crafted packets are engineered to appear as legitimate traffic while containing malicious content or payloads that would normally be blocked by the configured security policies. The vulnerability operates at the packet processing level where the detection engine fails to properly validate or evaluate certain traffic patterns that should trigger security alerts or blocking mechanisms. This algorithmic failure creates a pathway for malicious traffic to flow through the network without being properly identified or filtered according to the security rules that administrators have established.
The operational impact of this vulnerability extends beyond simple policy bypass to represent a significant compromise of network security posture. An unauthenticated remote attacker can leverage this vulnerability to deliver malicious payloads directly to protected network segments without triggering the expected security controls. This creates a scenario where network defenders lose visibility into potentially malicious activities that should be detected and blocked by their security infrastructure. The vulnerability essentially allows attackers to operate within networks that are supposed to be protected by Snort-based security policies, potentially enabling data exfiltration, lateral movement, or other malicious activities. The remote nature of the exploit means that attackers can operate from outside the network perimeter without requiring any authentication credentials, making the attack surface particularly concerning for organizations relying on these security controls.
Organizations affected by this vulnerability should prioritize immediate mitigation through official Cisco security advisories and patches that address the specific algorithmic flaw in the Snort detection engine. The recommended approach includes applying the latest security updates and firmware releases that contain fixes for the detection algorithm vulnerability. Network administrators should also implement additional monitoring and anomaly detection measures to identify potential exploitation attempts, as the vulnerability may not always be immediately apparent through standard security alerts. The mitigation strategy should also include reviewing and validating existing security policies to ensure that any bypassed protections are properly addressed through alternative security controls. Given the nature of this vulnerability, organizations should consider implementing network segmentation and additional layers of security monitoring to reduce the potential impact of successful exploitation attempts. This vulnerability aligns with CWE-284 Access Control Issues and represents a significant concern within the ATT&CK framework under Defense Evasion techniques where adversaries attempt to bypass security controls to maintain persistence and access within target networks.