CVE-2026-2157: D-Link DIR-823X Firmware RCE Vulnerability

CVE-2026-2157 Overview

CVE-2026-2157 is an operating system (OS) command injection vulnerability affecting the D-Link DIR-823X router running firmware version 250416. The flaw resides in the sub_4175CC function handling requests to /goform/set_static_route_table. An attacker can manipulate the interface, destip, netmask, gateway, or metric arguments to inject arbitrary shell commands. The vulnerability is remotely reachable over the network and the exploit details have been publicly disclosed, increasing the risk of opportunistic abuse against exposed devices.

Critical Impact

Authenticated remote attackers can inject operating system commands through the static route configuration endpoint, leading to full compromise of the router's confidentiality, integrity, and availability.

Affected Products

• D-Link DIR-823X router (hardware)
• D-Link DIR-823X firmware version 250416
• Deployments exposing the web management interface to untrusted networks

Discovery Timeline

• 2026-02-08 - CVE-2026-2157 published to the National Vulnerability Database (NVD)
• 2026-02-11 - Last updated in the NVD database

Technical Details for CVE-2026-2157

Vulnerability Analysis

The vulnerability is classified under CWE-77 (Improper Neutralization of Special Elements used in a Command) and CWE-78 (OS Command Injection). The affected handler sub_4175CC processes HTTP POST data submitted to the /goform/set_static_route_table endpoint without sanitizing shell metacharacters. The router subsequently passes user-controlled values to a system shell to apply routing configuration, enabling command execution in the router's underlying Linux environment.

Successful exploitation grants the attacker the ability to execute arbitrary binaries, modify firmware behavior, pivot into the internal network, or capture traffic traversing the device. The EPSS (Exploit Prediction Scoring System) score is 0.653% with a percentile of 71.1, reflecting elevated probability of exploitation activity relative to the broader CVE population.

Root Cause

The sub_4175CC function fails to validate or sanitize the interface, destip, netmask, gateway, and metric request parameters before they are concatenated into a shell command. Special characters such as ;, |, &&, and backticks are interpreted by the underlying shell rather than treated as literal route configuration data. This is a classic input validation failure in an embedded web application that invokes system utilities for network configuration.

Attack Vector

The attack is delivered over the network against the router's HTTP management interface. According to the CVSS 4.0 vector, the attacker must possess high privileges, indicating authentication to the device administrative interface is required. After authenticating, the attacker submits a crafted POST request to /goform/set_static_route_table containing shell metacharacters embedded within one of the affected parameters. The injected command executes with the privileges of the web server process, typically root on consumer-grade routers.

No verified proof-of-concept code is published in structured exploit databases at this time, though a public issue report exists on GitHub. Refer to the GitHub CVE Issue Report and the VulDB entry #344859 for additional technical context.

Detection Methods for CVE-2026-2157

Indicators of Compromise

• HTTP POST requests to /goform/set_static_route_table containing shell metacharacters such as ;, |, `, $(, or && in the interface, destip, netmask, gateway, or metric fields
• Unexpected child processes spawned by the router's goahead or httpd web server, such as sh, wget, curl, tftp, or nc
• Outbound connections from the router to unfamiliar hosts shortly after configuration changes
• Unauthorized modifications to the device static route table or firmware persistence locations

Detection Strategies

• Inspect router web access logs for POST requests to /goform/set_static_route_table and alert on parameter values containing non-routing characters
• Deploy network detection rules that match shell metacharacters appearing in form parameters destined for D-Link administrative endpoints
• Baseline normal egress from network infrastructure devices and alert on deviations such as router-initiated downloads or reverse shells

Monitoring Recommendations

• Forward router syslog and HTTP audit logs to a centralized logging platform for correlation
• Monitor for authentication events to the DIR-823X management UI from unexpected source addresses
• Track firmware version and configuration drift across managed D-Link devices

How to Mitigate CVE-2026-2157

Immediate Actions Required

• Restrict access to the router web management interface so it is reachable only from trusted internal hosts and never from the WAN
• Rotate administrator credentials on all DIR-823X devices and enforce strong, unique passwords to reduce the chance of an attacker satisfying the authenticated precondition
• Audit the static route table and recent configuration changes for unauthorized entries indicating prior exploitation
• Treat exposed DIR-823X units as suspect and consider replacing or isolating them until a fixed firmware is available

Patch Information

No vendor patch has been published in the references available at the time of writing. D-Link customers should monitor the D-Link Security Resources portal for firmware updates addressing the sub_4175CC handler in /goform/set_static_route_table. Apply any subsequent firmware release on affected DIR-823X devices as soon as it becomes available.

Workarounds

• Disable remote (WAN-side) administration on the DIR-823X and require management traffic to traverse a VPN
• Place the router behind an upstream firewall that filters HTTP and HTTPS access to its management ports from untrusted segments
• Segment the router from sensitive internal subnets so that a successful compromise does not yield lateral access to high-value assets
• Where feasible, replace the affected device with a model that has current vendor support and a published fix

# Example: block external access to the DIR-823X management interface using an upstream Linux firewall
# Replace 203.0.113.10 with the WAN IP of the router and 192.0.2.0/24 with your trusted admin subnet
iptables -A FORWARD -p tcp -d 203.0.113.10 --dport 80  -s 192.0.2.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d 203.0.113.10 --dport 443 -s 192.0.2.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d 203.0.113.10 --dport 80  -j DROP
iptables -A FORWARD -p tcp -d 203.0.113.10 --dport 443 -j DROP