CVE-2025-11338 – A buffer overflow vulnerability in D-Link DI-71... (How to Fix)

📋 TL;DR

A buffer overflow vulnerability in D-Link DI-7100G C1 routers allows remote attackers to execute arbitrary code by manipulating the 'openid' parameter in the webchat login component. This affects all versions up to September 28, 2025. Organizations using these routers with internet-facing web interfaces are at immediate risk.

💻 Affected Systems

Products:

D-Link DI-7100G C1

Versions: All versions up to 20250928

Operating Systems: Embedded Linux (router firmware)

Default Config Vulnerable: ⚠️ Yes

Notes: Vulnerability exists in default web interface configuration

📦 What is this software?

Di 7100g C1 Firmware by Dlink

View all CVEs affecting Di 7100g C1 Firmware →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution leading to full device compromise, network pivoting, and data exfiltration

🟠

Likely Case

Remote code execution resulting in device takeover and botnet recruitment

🟢

If Mitigated

Denial of service or device crash if exploit fails

🌐 Internet-Facing: HIGH - Exploit is remote and unauthenticated with public proof-of-concept

🏢 Internal Only: MEDIUM - Still exploitable from internal networks but attack surface reduced

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploit code has been published and targets specific buffer overflow in jhttpd component

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Unknown

Vendor Advisory: https://www.dlink.com/

Restart Required: Yes

Instructions:

1. Check D-Link security advisories for firmware updates
2. Download latest firmware from official D-Link support site
3. Upload firmware via router web interface
4. Reboot router after update

🔧 Temporary Workarounds

Disable web interface

all

Disable the vulnerable webchat/login.cgi endpoint

# Requires custom firewall rules or firmware modification
# Not directly supported by default configuration

Network segmentation

linux

Isolate router from internet and restrict internal access

# Configure firewall to block external access to router web interface
# Example: iptables -A INPUT -p tcp --dport 80 -j DROP
# Example: iptables -A INPUT -p tcp --dport 443 -j DROP

🧯 If You Can't Patch

Immediately disconnect affected routers from internet-facing networks
Implement strict network access controls allowing only trusted IPs to access router management interface

🔍 How to Verify

Check if Vulnerable:

Check router firmware version via web interface at System > Firmware or via SSH with 'cat /etc/version'

Check Version:

ssh admin@router-ip 'cat /etc/version' or check web interface System > Firmware

Verify Fix Applied:

Verify firmware version is newer than 20250928 and test webchat/login.cgi endpoint with controlled payload

📡 Detection & Monitoring

Log Indicators:

Unusual POST requests to /webchat/login.cgi with long openid parameters
Multiple failed login attempts from single source
Process crashes in jhttpd service

Network Indicators:

HTTP POST requests to /webchat/login.cgi with abnormally long parameters
Traffic patterns suggesting exploit delivery

SIEM Query:

source="router_logs" AND uri="/webchat/login.cgi" AND (method="POST" OR parameter_length>1000)

📊 Metadata

CVE ID: CVE-2025-11338

CVSS v3 Score: 8.8 (HIGH)

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

CWE: CWE-119

EPSS Score: 0.2% exploit probability (41.9th percentile)

Published: October 6, 2025

Last Updated: November 19, 2025

🔗 References

https://vuldb.com/?ctiid.327221 Permissions Required,VDB Entry
https://vuldb.com/?id.327221 Third Party Advisory,VDB Entry
https://vuldb.com/?submit.664619 Third Party Advisory,VDB Entry
https://www.dlink.com/ Product
https://www.yuque.com/jh0ng/vmpda6/kggo2ngrcphzvwml Permissions Required

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🔗 Related Vulnerabilities

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