D-Link DIR-825 Web Interface Buffer Overflow Pre-Authentication Remote Code Execution (RCE) (CVE-2020-29557)
Executive & SecOps Summary
SECOPS ASSESSMENTD-Link DIR-825 R1 devices running firmware versions up to 3.0.1 before 2020-11-20
Remote unauthenticated attackers can execute arbitrary code with root privileges by sending crafted HTTP requests, leading to complete device compromise
Apply the latest official firmware patch immediately, disable WAN-side remote management, or replace end-of-life hardware
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Upgrade the router firmware to the latest secure release provided by the vendor. Below is an example of downloading and applying the firmware via CLI.
# Download the patched firmware binary and verify its integrity
wget http://www.dlink.ru/ru/download2/5/19/2354/441/DIR_825_v3.0.1_release.bin
sha256sum DIR_825_v3.0.1_release.bin
# Example command to flash the firmware via device API
curl -X POST -F 'file=@DIR_825_v3.0.1_release.bin' http://192.168.0.1/cgi-bin/upgrade.cgi2. Temporary Workaround & Hardening Configuration
If patching cannot be applied immediately, disable remote WAN management and restrict access to the web interface to trusted internal IP addresses only.
# Block all incoming HTTP/HTTPS traffic from the WAN interface (e.g., eth0)
iptables -A INPUT -i eth0 -p tcp --dport 80 -j DROP
iptables -A INPUT -i eth0 -p tcp --dport 443 -j DROP
# Allow access only from a specific trusted administrator IP
iptables -A INPUT -s 192.168.0.100 -p tcp --dport 80 -j ACCEPT3. Log Audit & IoC Verification Commands
Verify the current firmware version and inspect web server logs for potential exploitation attempts.
# Check the current firmware build version\cat /etc/version
# Scan web server access logs for abnormally long request payloads indicating buffer overflow attempts
grep -E 'GET|POST' /var/log/httpd_access.log | awk 'length($0) > 500'Stop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
Eliminate public-facing VPN concentrators and firewall management ports with identity-first Zero-Trust Network Access.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2020-29557) is a critical stack-based buffer overflow (CWE-119) residing in the web management interface of D-Link DIR-825 R1 routers. The root cause is the lack of proper boundary validation on user-supplied input parameters within HTTP requests before copying them into a fixed-size memory buffer. This allows an attacker to overwrite the stack return address and hijack the execution flow.
2. Exploitation Mechanics & Attack Scenario
An attacker can exploit this vulnerability remotely without any authentication (Pre-auth). By sending a specially crafted HTTP POST or GET request containing an excessively long payload (shellcode) to the web server daemon, the attacker triggers a buffer overflow. This corrupts the stack memory, allowing the injected shellcode to execute under the context of the web server process, which typically runs with root privileges on embedded Linux devices.
3. Infrastructure & Business Impact
As this vulnerability is actively exploited in the wild and listed in the CISA KEV catalog, it poses a severe threat to enterprise and home networks. Successful exploitation grants full administrative control over the router, enabling attackers to intercept network traffic, perform DNS hijacking, deploy botnet malware, and pivot laterally into the internal corporate network.
Official Vendor Advisories & References
An issue was discovered on D-Link DIR-825 R1 devices through 3.0.1 before 2020-11-20. A buffer overflow in the web interface allows attackers to achieve pre-authentication remote code execution.
Frequently Asked SecOps Questions (CVE-2020-29557)
FAQQ1. How critical is CVE-2020-29557 and is it actively exploited in the wild?
CVE-2020-29557 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 55.8%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2020-29557?
Primary impacted vendors include d-link across dir-825. Scope summary: D-Link DIR-825 R1 devices running firmware versions 3.0.1 and prior (released before November 20, 2020)
Q3. What temporary mitigations or workarounds exist for CVE-2020-29557 before patching?
[Mitigation] Apply the latest official firmware patch immediately, disable WAN-side remote management, or replace end-of-life hardware Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2020-29557
Instantly format this advisory into an executive CISO summary or engineering patch ticket.
🔗 Related Advisories in Similar Stack (d-link)
View Category →D-Link DIR-505 Router TFTP File Upload Stack-Based Buffer Overflow (CVE-2026-120189) Technical Analysis and Mitigation Guide
[Affected Scope] D-Link DIR-505 firmware version 1.10B02 and prior
Citrix NetScaler ADC and Gateway Memory Overflow Vulnerability (CVE-2026-8452) Critical Security Advisory
[Affected Scope] Citrix NetScaler ADC and NetScaler Gateway appliances configured as a Gateway (SSL VPN, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server
Citrix NetScaler ADC and Gateway Remote Code Execution (RCE) and DoS Vulnerability (CVE-2026-88772)
[Affected Scope] Citrix NetScaler ADC and Gateway versions prior to 14.1-73.37 and 13.1-64.23, including FIPS/NDcPP editions.
Security Advisory for NetScaler ADC and Gateway Denial of Service (DoS) Vulnerability (CVE-2026-88779)
[Affected Scope] NetScaler ADC and Gateway versions prior to 14.1-73.41 and 13.1-64.28.
Subscribe to Daily Vulnerability Briefings & KEV Alerts
Concise morning briefings for SecOps, DevSecOps, and SRE teams covering newly exploited CVEs and mitigation priorities.