Snort 3 GRE Tunnel Decapsulation DoS Vulnerability

Executive Summary

This vulnerability affects Cisco products using the Snort 3 Detection Engine. It involves improper handling of nested GRE traffic, allowing an unauthenticated remote attacker to send crafted GRE payloads. This can cause the Snort 3 Detection Engine to restart unexpectedly, leading to a denial of service or bypass condition depending on device configuration.

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Detection Guidance

This vulnerability involves crafted GRE traffic triggering Snort 3 Detection Engine restarts. Monitor for unexpected Snort 3 engine reloads or crashes in logs. Check for GRE traffic anomalies using network monitoring tools like tcpdump or Wireshark to inspect GRE packet structures for malformed payloads.

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Impact Analysis

The vulnerability could disrupt network traffic inspection by causing the Snort 3 Detection Engine to restart unexpectedly. This may result in temporary loss of security monitoring, potential bypass of security controls, or denial of service for network services relying on the engine.

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Mitigation Strategies

Apply Cisco's official patches or updates for affected Snort 3 and Cisco products. Disable GRE tunnel decapsulation if not required. Implement rate limiting or filtering for GRE traffic. Monitor Snort 3 engine status and logs for unexpected restarts.

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