CVE-2025-25900
📋 TL;DR
A buffer overflow vulnerability exists in TP-Link TL-WR841ND V11 routers via the username and password parameters at /userRpm/PPPoEv6CfgRpm.htm. Attackers can exploit this to cause Denial of Service (DoS) by sending crafted packets. Only users of this specific router model and version are affected.
💻 Affected Systems
- TP-Link TL-WR841ND
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete router crash requiring physical reboot, disrupting all network connectivity for connected devices.
Likely Case
Router becomes unresponsive, requiring reboot to restore functionality, causing temporary network outage.
If Mitigated
If properly segmented and firewalled, impact limited to isolated network segment with minimal business disruption.
🎯 Exploit Status
Exploit requires authentication to web interface; buffer overflow in username/password parameters leads to DoS.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Not provided in CVE references
Restart Required: Yes
Instructions:
1. Check TP-Link support site for firmware updates for TL-WR841ND V11. 2. Download latest firmware. 3. Log into router web interface. 4. Navigate to System Tools > Firmware Upgrade. 5. Upload and apply firmware update. 6. Router will reboot automatically.
🔧 Temporary Workarounds
Disable PPPoEv6 Configuration Access
linuxRestrict access to the vulnerable endpoint using firewall rules or router configuration.
iptables -A INPUT -p tcp --dport 80 -m string --string "/userRpm/PPPoEv6CfgRpm.htm" --algo bm -j DROP
Change Default Credentials
allUse strong, unique credentials to prevent unauthorized access to router web interface.
🧯 If You Can't Patch
- Segment router on isolated network segment to limit blast radius if exploited
- Implement network monitoring for unusual traffic patterns to /userRpm/PPPoEv6CfgRpm.htm
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in web interface under System Tools > Firmware Upgrade. If version is V11 with no recent updates, assume vulnerable.Check Version:
curl -s http://router-ip/userRpm/LoginRpm.htm?Save=Save | grep -i firmwareVerify Fix Applied:
After firmware update, verify version has changed from V11 or check TP-Link security advisories for patched version.📡 Detection & Monitoring
Log Indicators:
- Multiple failed login attempts followed by POST requests to /userRpm/PPPoEv6CfgRpm.htm with unusually long parameters
- Router syslog entries showing crash/reboot events
Network Indicators:
- HTTP POST requests to /userRpm/PPPoEv6CfgRpm.htm with username/password parameters exceeding normal length (e.g., >100 characters)
- Sudden drop in router responsiveness followed by reboot
SIEM Query:
source="router_logs" AND (url="/userRpm/PPPoEv6CfgRpm.htm" AND (param_length(username)>100 OR param_length(password)>100))