CVE-2024-20508

Q: What is the severity of CVE-2024-20508?

CVE-2024-20508 has a CVSS score of 5.8 (MEDIUM). An unauthenticated remote attacker can bypass security policies or cause denial of service on Cisco IOS XE devices with UTD Snort IPS Engine by sending crafted HTTP requests. This affects Cisco IOS XE Software with UTD Snort IPS Engine enabled. The vulnerability occurs due to insufficient HTTP request validation.

5.8 MEDIUM

Denial of Service

📋 TL;DR

An unauthenticated remote attacker can bypass security policies or cause denial of service on Cisco IOS XE devices with UTD Snort IPS Engine by sending crafted HTTP requests. This affects Cisco IOS XE Software with UTD Snort IPS Engine enabled. The vulnerability occurs due to insufficient HTTP request validation.

💻 Affected Systems

Products:

Cisco IOS XE Software with Unified Threat Defense (UTD) Snort Intrusion Prevention System (IPS) Engine

Versions: Specific affected versions detailed in Cisco advisory

Operating Systems: Cisco IOS XE

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects devices with Cisco UTD Snort IPS Engine enabled and configured to inspect HTTP traffic.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete bypass of all configured IPS security policies (if fail-open) or complete traffic disruption for inspected traffic (if fail-close), plus device instability from repeated Snort process reloads.

🟠

Likely Case

Intermittent Snort process crashes causing temporary security bypass or traffic disruption, potentially allowing malicious traffic through during fail-open periods.

🟢

If Mitigated

Limited to occasional Snort restarts with minimal traffic impact if proper network segmentation and monitoring are in place.

🌐 Internet-Facing: HIGH - Unauthenticated remote exploitation means internet-facing devices are directly vulnerable to attack.

🏢 Internal Only: MEDIUM - Internal attackers could still exploit, but requires network access to affected devices.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW - Crafted HTTP request through affected device

Exploitation requires sending traffic through the affected device, not direct device access.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Refer to Cisco advisory for specific fixed releases

Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-utd-snort3-dos-bypas-b4OUEwxD

Restart Required: Yes

Instructions:

1. Check current IOS XE version. 2. Review Cisco advisory for fixed releases. 3. Download and install appropriate fixed release. 4. Reboot device after upgrade.

🔧 Temporary Workarounds

Disable UTD Snort IPS Engine

cisco-ios-xe

Temporarily disable the vulnerable component until patching can be completed

no utd engine standard threat

Configure fail-close behavior

cisco-ios-xe

Change from default fail-open to fail-close to prevent security bypass during exploitation

utd engine standard threat fail-close

🧯 If You Can't Patch

Implement network segmentation to limit traffic to affected devices
Enable strict monitoring for Snort process crashes and unexpected traffic patterns

🔍 How to Verify

Check if Vulnerable:

Check if device runs Cisco IOS XE with UTD Snort IPS Engine enabled using 'show utd engine standard threat status'

Check Version:

show version | include IOS XE

Verify Fix Applied:

Verify IOS XE version is updated to fixed release and UTD Snort IPS Engine is functioning normally

📡 Detection & Monitoring

Log Indicators:

Snort process crashes/reloads in system logs
UTD engine failure messages
Unexpected traffic bypassing IPS policies

Network Indicators:

Unusual HTTP traffic patterns through affected devices
Traffic that should be blocked passing through

SIEM Query:

source="cisco-ios-xe" AND (event_type="process_crash" AND process="snort" OR message="*UTD*engine*failure*")

📊 Metadata

CVE ID: CVE-2024-20508

CVSS v3 Score: 5.8 (MEDIUM)

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

CWE: CWE-122

Published: September 25, 2024

Last Updated: October 3, 2024

🔗 References

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-utd-snort3-dos-bypas-b4OUEwxD Vendor Advisory

📋 TL;DR

💻 Affected Systems

📦 What is this software?

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

Unified Threat Defense Snort Intrusion Prevention System Engine by Cisco

⚠️ Risk & Real-World Impact

Worst Case

Likely Case

If Mitigated

🎯 Exploit Status

🛠️ Fix & Mitigation

✅ Official Fix

Instructions:

🔧 Temporary Workarounds

Disable UTD Snort IPS Engine

Configure fail-close behavior

🧯 If You Can't Patch

🔍 How to Verify

Check if Vulnerable:

Check Version:

Verify Fix Applied:

📡 Detection & Monitoring

Log Indicators:

Network Indicators:

SIEM Query:

📊 Metadata

🔗 References

📤 Share & Export

🔗 Related Vulnerabilities