CVE-2026-20025: Cisco Firewall OSPF DoS Vulnerability

CVE-2026-20025 Overview

A vulnerability in the OSPF protocol of Cisco Secure Firewall ASA Software and Cisco Secure FTD Software could allow an authenticated, adjacent attacker to cause an affected device to reload unexpectedly, resulting in a Denial of Service (DoS) condition. This vulnerability stems from insufficient input validation when processing OSPF link-state update (LSU) packets, which can lead to heap corruption.

Critical Impact

An attacker with the OSPF secret key can send crafted OSPF LSU packets to corrupt the heap and cause device reload, disrupting network security operations.

Affected Products

• Cisco Secure Firewall ASA Software
• Cisco Secure Firewall Threat Defense (FTD) Software
• Devices running vulnerable versions with OSPF configured

Discovery Timeline

• 2026-03-04 - CVE-2026-20025 published to NVD
• 2026-03-05 - Last updated in NVD database

Technical Details for CVE-2026-20025

Vulnerability Analysis

This vulnerability (CWE-190: Integer Overflow) exists in the OSPF protocol implementation within Cisco Secure Firewall products. The flaw occurs due to insufficient input validation when processing OSPF link-state update (LSU) packets. When specially crafted LSU packets are received by an affected device, the insufficient validation allows an integer overflow condition to occur, which subsequently corrupts heap memory.

The exploitation requires adjacency to the affected device on the network and possession of the OSPF secret key used for authentication. While these prerequisites limit the attack surface, successful exploitation results in complete device reload, effectively taking the firewall offline and potentially exposing the protected network during the outage.

Root Cause

The root cause is an integer overflow vulnerability (CWE-190) in the OSPF LSU packet processing code. The software fails to properly validate numeric input fields within LSU packets before using them in memory operations. When an attacker supplies maliciously crafted values that cause an integer overflow, subsequent heap memory operations write data to unintended memory locations, corrupting the heap and causing the device to crash.

Attack Vector

The attack requires adjacent network access, meaning the attacker must be on the same network segment as the vulnerable device. Additionally, the attacker must possess the OSPF secret key to authenticate their malicious packets. The attack flow involves:

1. The attacker establishes OSPF adjacency with the target firewall using a compromised or stolen OSPF secret key
2. Crafted OSPF LSU packets are constructed with values designed to trigger the integer overflow
3. Upon receipt and processing, the vulnerable code fails to validate the input properly
4. The integer overflow leads to heap corruption during memory operations
5. The device crashes and reloads, causing a denial of service condition

For detailed technical information regarding this vulnerability, refer to the Cisco Security Advisory.

Detection Methods for CVE-2026-20025

Indicators of Compromise

• Unexpected device reloads or crashes on Cisco ASA or FTD appliances
• Crash logs indicating heap corruption in OSPF-related processes
• Unusual OSPF LSU packet activity from non-standard or unauthorized sources
• OSPF adjacency attempts from unexpected network locations

Detection Strategies

• Monitor system logs for repeated device reloads or crash events mentioning OSPF or heap corruption
• Implement network monitoring to detect anomalous OSPF traffic patterns or malformed LSU packets
• Review OSPF adjacency tables for unauthorized or suspicious neighbors
• Enable OSPF authentication logging to track authentication attempts

Monitoring Recommendations

• Configure syslog forwarding to a SIEM solution for centralized analysis of device crash events
• Implement network traffic analysis for OSPF protocol monitoring (protocol 89)
• Set up alerts for multiple device reloads within a short timeframe
• Monitor for OSPF configuration changes that could indicate key compromise

How to Mitigate CVE-2026-20025

Immediate Actions Required

• Review the Cisco Security Advisory for affected versions and available patches
• Audit and rotate OSPF secret keys to limit exposure from compromised credentials
• Review OSPF neighbor configurations and remove unauthorized adjacencies
• Implement network segmentation to limit adjacent network access to firewalls

Patch Information

Cisco has released security updates to address this vulnerability. Administrators should consult the Cisco Security Advisory for specific version information, fixed releases, and upgrade paths for both Cisco Secure Firewall ASA Software and Cisco Secure FTD Software.

Workarounds

• Restrict physical and logical access to network segments adjacent to vulnerable devices
• Implement strict OSPF authentication and ensure secret keys are rotated regularly
• Consider disabling OSPF if not required for network operations until patches can be applied
• Deploy high-availability configurations to minimize service disruption during potential exploitation

# Example: Verify OSPF authentication configuration on Cisco ASA
show running-config router ospf
show ospf neighbor
show ospf interface

# Monitor for crash events
show crashinfo
show logging | include reload|crash|OSPF