CVE-2016-5681 – This CVE describes a critical stack-based buffe... (How to Fix)

Q: What is the severity of CVE-2016-5681?

CVE-2016-5681 has a CVSS score of 9.8 (CRITICAL). This CVE describes a critical stack-based buffer overflow vulnerability in D-Link router web interfaces that allows remote attackers to execute arbitrary code by sending an overly long session cookie. Attackers can gain full control of affected routers without authentication. Affected users include anyone using vulnerable D-Link DIR series routers with exposed web management interfaces.

📋 TL;DR

This CVE describes a critical stack-based buffer overflow vulnerability in D-Link router web interfaces that allows remote attackers to execute arbitrary code by sending an overly long session cookie. Attackers can gain full control of affected routers without authentication. Affected users include anyone using vulnerable D-Link DIR series routers with exposed web management interfaces.

💻 Affected Systems

Products:

D-Link DIR-850L B1
DIR-817 Ax
DIR-818LW Bx
DIR-822 C1
DIR-823 A1
DIR-895L A1
DIR-890L A1
DIR-885L A1
DIR-880L A1
DIR-868L B1
DIR-868L C1

Versions: See specific version ranges in CVE description (e.g., DIR-850L B1 before 2.07WWB05)

Operating Systems: Router firmware

Default Config Vulnerable: ⚠️ Yes

Notes: All default configurations are vulnerable. Web management interface typically enabled by default.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete compromise of router with persistent backdoor installation, credential theft, network traffic interception, and pivot to internal network devices.

🟠

Likely Case

Router takeover leading to DNS hijacking, credential harvesting, and use as attack platform against internal network.

🟢

If Mitigated

No impact if router is patched or web interface is not internet-accessible.

🌐 Internet-Facing: HIGH - Remote unauthenticated exploit against internet-exposed routers.

🏢 Internal Only: MEDIUM - Requires attacker to be on local network or have compromised internal host.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: CONFIRMED

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Simple buffer overflow with public exploit code available. No authentication required.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: See specific fixed versions in CVE description (e.g., DIR-850L B1 2.07WWB05)

Vendor Advisory: http://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10063

Restart Required: Yes

Instructions:

1. Download latest firmware from D-Link support site for your specific model. 2. Log into router web interface. 3. Navigate to Tools > Firmware. 4. Upload firmware file. 5. Wait for reboot (do not interrupt power).

🔧 Temporary Workarounds

Disable remote management

all

Prevent internet access to router web interface

Network segmentation

all

Isolate router management interface to separate VLAN

🧯 If You Can't Patch

Replace affected routers with newer models or different vendors
Implement strict firewall rules blocking all external access to router web interface (ports 80/443)

🔍 How to Verify

Check if Vulnerable:

Check router firmware version via web interface (Status > Device Info) and compare with patched versions listed in CVE.

Check Version:

No CLI command - check via web interface or router label

Verify Fix Applied:

Confirm firmware version matches or exceeds patched version listed in vendor advisory.

📡 Detection & Monitoring

Log Indicators:

Unusually long HTTP cookie values in web server logs
Multiple failed login attempts with malformed cookies

Network Indicators:

HTTP POST requests to /dws/api/Login with oversized cookies
Sudden outbound connections from router to suspicious IPs

SIEM Query:

http.url:"/dws/api/Login" AND http.cookie.length > 1000

📊 Metadata

CVE ID: CVE-2016-5681

CVSS v3 Score: 9.8 (CRITICAL)

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

CWE: CWE-119

Published: August 25, 2016

Last Updated: April 12, 2025

🔗 References

http://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10063 Vendor Advisory
http://www.kb.cert.org/vuls/id/332115 Third Party Advisory,US Government Resource
http://www.securityfocus.com/bid/92427 Third Party Advisory,VDB Entry
http://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10063 Vendor Advisory
http://www.kb.cert.org/vuls/id/332115 Third Party Advisory,US Government Resource
http://www.securityfocus.com/bid/92427 Third Party Advisory,VDB Entry

📤 Share & Export

📄 Export Markdown 📋 Export JSON

🔗 Related Vulnerabilities

If you're affected by CVE-2016-5681, you might also want to check these: