CVE-2026-20027: Snort 3 Information Disclosure Vulnerability

CVE-2026-20027 Overview

Multiple Cisco products are affected by a vulnerability in the processing of DCE/RPC requests that could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to leak sensitive information or to restart, resulting in an interruption of packet inspection.

This vulnerability is due to an error in buffer handling logic when processing DCE/RPC requests, which can result in a buffer out-of-bounds read. An attacker could exploit this vulnerability by sending a large number of DCE/RPC requests through an established connection that is inspected by Snort 3. A successful exploit could allow the attacker to obtain sensitive information in the Snort 3 data stream.

Critical Impact

Unauthenticated remote attackers can exploit improper buffer handling in Snort 3's DCE/RPC processing to leak sensitive information from memory or cause service interruption, compromising network security monitoring capabilities.

Affected Products

• Multiple Cisco products running Snort 3 Detection Engine
• Cisco Firepower Threat Defense (FTD) with Snort 3 enabled
• Cisco products utilizing Snort 3 for DCE/RPC inspection

Discovery Timeline

• 2026-01-07 - CVE-2026-20027 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2026-20027

Vulnerability Analysis

This vulnerability stems from improper buffer handling logic within the Snort 3 Detection Engine when processing DCE/RPC (Distributed Computing Environment / Remote Procedure Calls) network traffic. The flaw is classified as CWE-200 (Information Exposure), manifesting through an out-of-bounds read condition that occurs during the inspection of DCE/RPC protocol packets.

When Snort 3 processes DCE/RPC requests, the buffer handling routines fail to properly validate boundary conditions, allowing read operations to access memory beyond the intended buffer limits. This enables attackers to extract sensitive information that may be present in adjacent memory regions within the Snort 3 process space.

The vulnerability requires no authentication and can be exploited remotely over the network. While the impact is primarily limited to information disclosure with no integrity or availability impact to the underlying system, the exposure of data within the Snort 3 inspection engine could reveal network traffic patterns, inspection rules, or other security-sensitive information.

Root Cause

The root cause is a buffer boundary validation error in the DCE/RPC request processing routines within Snort 3. The detection engine fails to properly check buffer limits when handling malformed or specially crafted DCE/RPC packets, resulting in out-of-bounds memory read operations. This improper input validation allows the engine to read beyond allocated buffer space when parsing DCE/RPC protocol data structures.

Attack Vector

The attack is network-based and requires no user interaction or privileges. An attacker exploits this vulnerability by:

1. Establishing a network connection that passes through a device running Snort 3 inspection
2. Sending a large volume of specially crafted DCE/RPC requests through the established connection
3. Triggering the out-of-bounds read condition in the Snort 3 buffer handling logic
4. Extracting sensitive information leaked into the Snort 3 data stream

The attack leverages the DCE/RPC protocol inspection functionality, meaning any network path where Snort 3 performs deep packet inspection of DCE/RPC traffic is potentially vulnerable. The attacker does not need direct access to the Cisco device itself—only the ability to send traffic through it.

Detection Methods for CVE-2026-20027

Indicators of Compromise

• Unusual volume of DCE/RPC traffic patterns traversing network inspection points
• Snort 3 Detection Engine crashes or unexpected restarts
• Abnormal memory consumption patterns in Snort 3 processes
• Suspicious outbound data streams following heavy DCE/RPC activity

Detection Strategies

• Monitor Snort 3 process stability and log unexpected service restarts or crashes
• Implement network traffic analysis to detect anomalous DCE/RPC request volumes
• Enable detailed logging for DCE/RPC protocol inspection events
• Configure alerting for Snort 3 engine memory exceptions or buffer-related errors

Monitoring Recommendations

• Review Cisco Firepower Management Center logs for Snort 3 engine health indicators
• Establish baseline DCE/RPC traffic patterns to identify statistical anomalies
• Monitor system logs on devices running Snort 3 for segmentation faults or memory access violations
• Implement network segmentation monitoring to detect lateral movement attempts following information disclosure

How to Mitigate CVE-2026-20027

Immediate Actions Required

• Review the Cisco Security Advisory for affected product versions and available patches
• Assess which Cisco products in your environment utilize Snort 3 Detection Engine with DCE/RPC inspection enabled
• Prioritize patching based on network exposure and criticality of the inspection points
• Consider temporarily disabling DCE/RPC inspection if the risk is unacceptable and patching is delayed

Patch Information

Cisco has released security updates to address this vulnerability. Administrators should consult the Cisco Security Advisory for specific patch versions and upgrade paths for affected products. The advisory provides detailed instructions for identifying vulnerable software versions and obtaining the appropriate updates.

Workarounds

• Evaluate whether DCE/RPC inspection can be temporarily disabled on affected Snort 3 deployments
• Implement network segmentation to limit exposure of vulnerable inspection points
• Deploy additional network monitoring at chokepoints to detect exploitation attempts
• Consider routing DCE/RPC traffic through alternative inspection mechanisms until patches are applied

# Example: Check Snort 3 version on Cisco FTD
# Access the FTD CLI and verify the current Snort version
show snort3 engine version

# Review active inspection policies for DCE/RPC
show running-config policy-map | include dcerpc