CVE-2021-26827 – A buffer overflow vulnerability in TP-Link WR20... (How to Fix)

Q: What is the severity of CVE-2021-26827?

CVE-2021-26827 has a CVSS score of 7.5 (HIGH). A buffer overflow vulnerability in TP-Link WR2041 v1 router firmware allows remote attackers to crash the router by sending a specially crafted HTTP request with an overly long SSID parameter. This affects users of TP-Link WR2041 v1 routers running vulnerable firmware versions. The vulnerability results in denial-of-service, disrupting network connectivity.

📋 TL;DR

A buffer overflow vulnerability in TP-Link WR2041 v1 router firmware allows remote attackers to crash the router by sending a specially crafted HTTP request with an overly long SSID parameter. This affects users of TP-Link WR2041 v1 routers running vulnerable firmware versions. The vulnerability results in denial-of-service, disrupting network connectivity.

💻 Affected Systems

Products:

TP-Link WR2041 v1
TP-Link TL-WR2041+

Versions: All firmware versions prior to patch

Operating Systems: Embedded router firmware

Default Config Vulnerable: ⚠️ Yes

Notes: Affects the web management interface which is typically enabled by default on these routers.

📦 What is this software?

Tl Wr2041\+ Firmware by Tp Link

View all CVEs affecting Tl Wr2041\+ Firmware →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Router becomes completely unresponsive, requiring physical power cycle to restore functionality, causing extended network downtime.

🟠

Likely Case

Router crashes and reboots automatically or requires manual restart, causing temporary network disruption.

🟢

If Mitigated

If patched or workarounds applied, no impact beyond normal operation.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploit requires sending a single HTTP request with long parameter, making it trivial to execute.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Check TP-Link support for latest firmware

Vendor Advisory: https://www.tp-link.com/us/support/download/tl-wr2041+/#Firmware

Restart Required: Yes

Instructions:

1. Visit TP-Link support page for TL-WR2041+
2. Download latest firmware
3. Log into router web interface
4. Navigate to System Tools > Firmware Upgrade
5. Upload and install new firmware
6. Wait for router to reboot

🔧 Temporary Workarounds

Disable Remote Management

all

Prevent external access to router web interface

Change Default Admin Credentials

all

Use strong unique credentials for router administration

🧯 If You Can't Patch

Disable the web management interface entirely
Place router behind firewall with strict inbound rules

🔍 How to Verify

Check if Vulnerable:

Check firmware version in router web interface under System Tools > Firmware Upgrade

Check Version:

Check router web interface or use nmap scan on port 80/443

Verify Fix Applied:

Verify firmware version matches latest available from TP-Link

📡 Detection & Monitoring

Log Indicators:

HTTP requests to /userRpm/popupSiteSurveyRpm.html with unusually long parameters
Router crash/reboot events in system logs

Network Indicators:

Multiple HTTP POST requests to router management interface with long payloads
Sudden loss of router connectivity

SIEM Query:

source="router_logs" AND (uri="/userRpm/popupSiteSurveyRpm.html" AND content_length>1000)

📊 Metadata

CVE ID: CVE-2021-26827

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: April 14, 2021

Last Updated: November 21, 2024

🔗 References

https://github.com/GD008/vuln/blob/main/tplink_wr2041/tplink_WR2041pv1.md Exploit,Third Party Advisory
https://github.com/GD008/vuln/blob/main/tplink_wr2041/tplink_WR2041pv1.md Exploit,Third Party Advisory

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🔗 Related Vulnerabilities

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