CVE-2024-20376

Q: What is the severity of CVE-2024-20376?

CVE-2024-20376 has a CVSS score of 7.5 (HIGH). An unauthenticated remote attacker can send a crafted request to the web-based management interface of vulnerable Cisco IP Phone firmware, causing the device to reload and creating a denial-of-service condition. This affects organizations using Cisco IP Phones with vulnerable firmware versions. The vulnerability stems from insufficient input validation in the web interface.

7.5 HIGH

Denial of Service

📋 TL;DR

An unauthenticated remote attacker can send a crafted request to the web-based management interface of vulnerable Cisco IP Phone firmware, causing the device to reload and creating a denial-of-service condition. This affects organizations using Cisco IP Phones with vulnerable firmware versions. The vulnerability stems from insufficient input validation in the web interface.

💻 Affected Systems

Products:

Cisco IP Phone 7800 Series
Cisco IP Phone 8800 Series

Versions: Firmware versions prior to 14.2(1)SR1

Operating Systems: Cisco IP Phone firmware

Default Config Vulnerable: ⚠️ Yes

Notes: Devices with web-based management interface enabled are vulnerable. Some configurations may have this disabled by default.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Persistent DoS attacks could render phone systems unusable, disrupting business communications and operations.

🟠

Likely Case

Intermittent phone outages requiring manual reboots, causing temporary communication disruptions.

🟢

If Mitigated

Minimal impact with proper network segmentation and access controls limiting exposure.

🌐 Internet-Facing: HIGH - Unauthenticated remote exploitation makes internet-facing devices particularly vulnerable.

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

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

The vulnerability requires sending crafted HTTP requests to the web interface, which is relatively straightforward for attackers with network access.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Firmware 14.2(1)SR1 and later

Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ipphone-multi-vulns-cXAhCvS

Restart Required: Yes

Instructions:

1. Download firmware 14.2(1)SR1 or later from Cisco. 2. Upload to phone via TFTP or HTTP. 3. Reboot phone to apply update. 4. Verify firmware version after reboot.

🔧 Temporary Workarounds

Disable Web Interface

all

Disable the web-based management interface to prevent exploitation.

configure terminal
telephony-service
no web admin

Network Segmentation

all

Restrict access to phone management interfaces using firewall rules.

🧯 If You Can't Patch

Implement strict network access controls to limit who can reach the phone management interfaces
Monitor for unusual HTTP requests to phone management ports and implement rate limiting

🔍 How to Verify

Check if Vulnerable:

Check firmware version via phone web interface or console: Settings > Status > Firmware Information

Check Version:

From phone: Press Settings button > Status > Firmware Information

Verify Fix Applied:

Confirm firmware version is 14.2(1)SR1 or later and test web interface functionality

📡 Detection & Monitoring

Log Indicators:

Multiple HTTP requests to phone management interface followed by device reboots
Unusual HTTP request patterns to /CGI/ endpoints

Network Indicators:

HTTP requests with malformed parameters to phone management ports (typically 80/443)
Sudden increase in phone reboot events

SIEM Query:

source="phone_logs" AND (http_request="*CGI*" OR event="reboot") AND count>10

📊 Metadata

CVE ID: CVE-2024-20376

CVSS v3 Score: 7.5 (HIGH)

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

CWE: CWE-787

Published: May 1, 2024

Last Updated: January 5, 2026

📋 TL;DR

💻 Affected Systems

📦 What is this software?

Ip Phone 6821 With Multiplatform Firmware by Cisco

Ip Phone 6841 With Multiplatform Firmware by Cisco

Ip Phone 6851 With Multiplatform Firmware by Cisco

Ip Phone 6861 With Multiplatform Firmware by Cisco

Ip Phone 6871 With Multiplatform Firmware by Cisco

Ip Phone 7811 With Multiplatform Firmware by Cisco

Ip Phone 7821 With Multiplatform Firmware by Cisco

Ip Phone 7832 With Multiplatform Firmware by Cisco

Ip Phone 7841 With Multiplatform Firmware by Cisco

Ip Phone 7861 With Multiplatform Firmware by Cisco

Ip Phone 8811 With Multiplatform Firmware by Cisco

Ip Phone 8832 With Multiplatform Firmware by Cisco

Ip Phone 8841 With Multiplatform Firmware by Cisco

Ip Phone 8845 With Multiplatform Firmware by Cisco

Ip Phone 8851 With Multiplatform Firmware by Cisco

Ip Phone 8861 With Multiplatform Firmware by Cisco

Ip Phone 8865 With Multiplatform Firmware by Cisco

Video Phone 8875 Firmware by Cisco