🔒 CVE-2025-20343: Cisco ISE RADIUS Suppression DoS Vulnerability 🌐

⚠️ Overview

🚨 High-severity denial-of-service (DoS) flaw in Cisco Identity Services Engine (ISE)!
💥 An unauthenticated remote attacker can crash the device with crafted RADIUS packets.
📅 Disclosed: November 5, 2025
✅ No known exploitation in the wild (yet!)

🛠️ How It Works

🔄 A logic error in the "Reject RADIUS requests from clients with repeated failures" setting.
🕵️‍♂️ Attacker sends crafted RADIUS Access-Requests targeting a rejected MAC address.
💣 Triggers unexpected restart → DoS condition
🌍 Requires network access to RADIUS port — no auth needed!

CWE-697: Incorrect Comparison Logic

📊 Severity Score

🔴 CVSS v3.1: 8.6 (High)

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

🖥️ Affected Systems

Product: Cisco Identity Services Engine (ISE)
Vulnerable Versions:

• 3.4.0
• 3.4 Patch 1
• 3.4 Patch 2
• 3.4 Patch 3

Only if using RADIUS (802.1X, VPN, etc.)
HA clusters may reduce downtime via failover

🛡️ Exploitation Status

🛑 Mitigation & Fixes

🔧 Fix It

• Upgrade to patched ISE version (check Cisco advisory)
• 📌 Apply ASAP — easy to exploit!

🔥 Workarounds

• Disable “Reject repeated failures” (⚠️ reduces brute-force protection)
• Filter RADIUS traffic with ACLs/firewalls
• Deploy HA with tested failover

🛡️ Best Practices

• 🧪 Test patches in lab first
• 📡 Monitor for: restarts, RADIUS spikes, auth failures
• ⏰ Patch during maintenance windows

📚 References

• 🔗 Cisco Official Advisory
• 📰 RedPacket Security
• 💻 BleepingComputer
• 🇩🇪 Heise Online

⚡ Action Item: If you run Cisco ISE 3.4, patch now! This is a low-effort, high-impact attack waiting to happen. 🚀

Stay secure! 🔐