CVE-2023-39745 – This buffer overflow vulnerability in TP-Link w... (How to Fix)

Q: What is the severity of CVE-2023-39745?

CVE-2023-39745 has a CVSS score of 7.5 (HIGH). This buffer overflow vulnerability in TP-Link wireless routers allows attackers to cause Denial of Service (DoS) by sending specially crafted GET requests to the /userRpm/AccessCtrlAccessRulesRpm component. Affected users include anyone using vulnerable TP-Link TL-WR940N V2, TL-WR941ND V5, or TL-WR841N V8 routers with default configurations.

📋 TL;DR

This buffer overflow vulnerability in TP-Link wireless routers allows attackers to cause Denial of Service (DoS) by sending specially crafted GET requests to the /userRpm/AccessCtrlAccessRulesRpm component. Affected users include anyone using vulnerable TP-Link TL-WR940N V2, TL-WR941ND V5, or TL-WR841N V8 routers with default configurations.

💻 Affected Systems

Products:

TP-Link TL-WR940N V2
TP-Link TL-WR941ND V5
TP-Link TL-WR841N V8

Versions: All firmware versions prior to patch

Operating Systems: Embedded router firmware

Default Config Vulnerable: ⚠️ Yes

Notes: Vulnerability exists in default configuration. Web interface typically accessible on port 80/443.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete router crash requiring physical reboot, potentially disrupting all network connectivity for extended periods.

🟠

Likely Case

Router becomes unresponsive, requiring manual reboot to restore functionality.

🟢

If Mitigated

No impact if router is behind firewall blocking external access to web interface.

🌐 Internet-Facing: HIGH - Default configurations expose web interface to WAN, making routers directly accessible from internet.

🏢 Internal Only: MEDIUM - Attackers on local network can exploit via LAN interface.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Simple GET request exploitation with public technical details available.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Check TP-Link support for latest firmware

Vendor Advisory: https://www.tp-link.com/support/download/

Restart Required: Yes

Instructions:

1. Visit TP-Link support site. 2. Download latest firmware for your model. 3. Log into router web interface. 4. Navigate to System Tools > Firmware Upgrade. 5. Upload and install new firmware. 6. Wait for automatic reboot.

🔧 Temporary Workarounds

Disable Remote Management

all

Prevent external access to router web interface

Change Default Admin Credentials

all

Mitigate unauthorized access attempts

🧯 If You Can't Patch

Place router behind firewall blocking inbound access to ports 80/443
Disable UPnP and ensure no port forwarding to router management interface

🔍 How to Verify

Check if Vulnerable:

Check router model and firmware version via web interface at 192.168.0.1 or 192.168.1.1

Check Version:

curl -s http://router-ip/userRpm/LoginRpm.htm | grep -i firmware

Verify Fix Applied:

Verify firmware version matches latest from TP-Link support site

📡 Detection & Monitoring

Log Indicators:

Multiple failed access attempts to /userRpm/AccessCtrlAccessRulesRpm
Router reboot events without user action

Network Indicators:

Unusual GET requests to router management interface
Traffic patterns suggesting DoS attempts

SIEM Query:

source="router.log" AND (uri="/userRpm/AccessCtrlAccessRulesRpm" OR event="reboot")

📊 Metadata

CVE ID: CVE-2023-39745

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-120

Published: August 21, 2023

Last Updated: November 21, 2024

🔗 References

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