CVE-2020-29557 Overview
A critical buffer overflow vulnerability exists in the web interface of D-Link DIR-825 R1 devices running firmware through version 3.0.1. This pre-authentication remote code execution vulnerability allows unauthenticated attackers to execute arbitrary code on affected devices via the network. The vulnerability has been actively exploited in the wild and is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, making immediate remediation essential for organizations with affected hardware.
Critical Impact
Pre-authentication remote code execution allows attackers to take complete control of vulnerable D-Link routers without any credentials, potentially compromising entire network segments and enabling lateral movement.
Affected Products
- D-Link DIR-825 R1 Firmware (versions through 3.0.1 before 2020-11-20)
- D-Link DIR-825/A (Hardware revision D1A)
- D-Link DIR-825/AC (Hardware revisions E, E1A)
- D-Link DIR-825/ACF (Hardware revision F1)
- D-Link DIR-825/GF (Hardware revision GF)
Discovery Timeline
- 2021-01-29 - CVE-2020-29557 published to NVD
- 2025-11-07 - Last updated in NVD database
Technical Details for CVE-2020-29557
Vulnerability Analysis
This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), commonly known as a buffer overflow. The flaw resides in the web interface of the D-Link DIR-825 R1 router, where insufficient bounds checking on user-supplied input allows attackers to overflow memory buffers and gain control of program execution.
The pre-authentication nature of this vulnerability is particularly dangerous because attackers can exploit it without needing valid credentials. By sending specially crafted HTTP requests to the router's web management interface, an attacker can overwrite critical memory regions, ultimately achieving arbitrary code execution with the privileges of the web server process—typically root on embedded devices like consumer routers.
Root Cause
The root cause stems from improper memory handling in the web interface's request processing logic. The firmware fails to properly validate the length of user-supplied data before copying it into fixed-size buffers. This classic buffer overflow pattern allows attackers to overwrite adjacent memory, including return addresses and function pointers, enabling control flow hijacking.
Attack Vector
The attack vector is network-based and requires no authentication or user interaction. An attacker with network access to the router's web management interface (typically accessible on the LAN, and potentially exposed to the WAN if remote management is enabled) can send malicious HTTP requests to trigger the overflow.
The exploitation flow typically involves:
- Identifying a vulnerable D-Link DIR-825 device on the network
- Crafting an HTTP request with oversized input fields targeting the vulnerable buffer
- Overwriting memory to redirect execution to attacker-controlled shellcode
- Achieving remote code execution with elevated privileges on the router
For detailed technical analysis of this vulnerability, refer to the GitHub D-Link Security Research page.
Detection Methods for CVE-2020-29557
Indicators of Compromise
- Unusual outbound connections from router management interfaces to unknown IP addresses
- Unexpected changes to router configurations, including DNS settings and firewall rules
- Anomalous HTTP request patterns to the router's web interface with oversized parameters
- Presence of unauthorized firmware modifications or persistent backdoors on the device
Detection Strategies
- Monitor network traffic for malformed HTTP requests targeting D-Link router web interfaces
- Implement intrusion detection signatures for known D-Link DIR-825 exploitation patterns
- Deploy network segmentation to isolate management interfaces from untrusted networks
- Review router logs for suspicious authentication attempts or configuration changes
Monitoring Recommendations
- Enable logging on D-Link devices and forward logs to a centralized SIEM for analysis
- Monitor for unusual traffic patterns on ports 80/443 associated with router management
- Implement network-based anomaly detection for embedded device communication patterns
- Regularly audit network inventory to identify unpatched D-Link devices
How to Mitigate CVE-2020-29557
Immediate Actions Required
- Update D-Link DIR-825 R1 firmware to the patched version released after 2020-11-20
- Disable remote management features if not required to reduce attack surface
- Isolate affected routers on a separate network segment until patching is complete
- Review the CISA Known Exploited Vulnerability entry for additional guidance
Patch Information
D-Link has released firmware updates to address this vulnerability. Updated firmware versions are available from the D-Link Firmware Download Page. Organizations should verify the firmware version on all DIR-825 devices and apply updates to any device running firmware version 3.0.1 or earlier that was released before November 20, 2020.
Given that this vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog, federal agencies and organizations following CISA guidance should prioritize remediation according to applicable binding operational directives.
Workarounds
- Disable the web management interface entirely if firmware updates cannot be immediately applied
- Restrict access to the router's management interface using firewall rules to allow only trusted IP addresses
- Consider replacing end-of-life or unsupported D-Link hardware with actively maintained alternatives
- Implement network-level controls such as VLANs to limit exposure of management interfaces
# Example: Restrict management access via iptables on upstream firewall
# Block external access to router management interface
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 443 -j DROP
# Allow management only from trusted admin workstation
iptables -I FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
