CVE-2025-7836: Critical Command Injection Vulnerability in D-Link DIR-816L Routers

A critical vulnerability has been discovered in D-Link DIR-816L routers, potentially allowing attackers to remotely execute arbitrary commands. This could lead to complete control over the device and potentially the entire network. This post will delve into the details of CVE-2025-7836 and offer recommendations for mitigation.

🔍 TL;DR Summary

D-Link DIR-816L routers are vulnerable to remote command injection due to improper handling of environment variables. Attackers can exploit this flaw to execute arbitrary commands on the router. A proof-of-concept exploit is publicly available, and users of affected devices should take immediate action.

🚨 Vulnerability Details

CVE ID: CVE-2025-7836
Description: A command injection vulnerability exists in the lxmldbc_system function within the /htdocs/cgibin component of D-Link DIR-816L routers. The vulnerability stems from insufficient sanitization of user-supplied data when handling environment variables.
CVSS Score and Vector:
- CVSS 3.1: 6.3 (Medium) CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
- CVSS 2.0: 6.5 (Medium) AV:N/AC:L/Au:S/C:P/I:P/A:P
The CVSS score indicates a medium severity. An attacker with low privileges on the network can remotely exploit this vulnerability without user interaction, potentially gaining partial control over the router's confidentiality, integrity, and availability. The older CVSS v2 score reflects similar concerns.
Exploit Requirements: An attacker needs to be on the same network as the router or have remote access through exposed management interfaces. Low privileges are needed.
Affected Vendor, Product, Version: D-Link DIR-816L up to version 2.06B01. It's important to note that this product is no longer supported.
CWE:
- CWE-77: Improper Neutralization of Special Elements used in a Command ('Command Injection'). This means the router fails to properly sanitize input used to construct system commands, allowing an attacker to inject their own commands.
- CWE-74: Improper Neutralization of Special Elements in Output Used by Another Syntax ('Injection'). This indicates a broader class of injection vulnerabilities, where untrusted data is inserted into a context where it can be misinterpreted and executed.

📅 Timeline of Events

2025-07-19: CVE ID assigned and vulnerability reported.
2025-07-19: Public disclosure of the exploit.

🧠 Exploitability & Real-World Risk

The existence of a public exploit significantly increases the risk associated with this vulnerability. An attacker could leverage this exploit to gain unauthorized access to the router, potentially changing DNS settings to redirect traffic, installing malware, or using the router as a botnet node. Given the widespread use of D-Link routers, this vulnerability poses a substantial threat, especially for users who haven't changed the default credentials or enabled remote management without proper security measures.

🛠️ Recommendations

Due to the end-of-life status of the D-Link DIR-816L, official patches are unlikely to be released. Therefore, the following recommendations are crucial:

Discontinue Use: The most secure solution is to replace the D-Link DIR-816L with a supported and actively maintained router.
Disable Remote Management: If you cannot replace the router immediately, ensure that remote management is disabled.
Strong Password: Change the default administrator password to a strong, unique password.
Network Segmentation: Isolate the router on a separate network segment to limit the impact of a potential compromise.

🧪 Technical Insight

The vulnerability lies within the lxmldbc_system function, which is responsible for executing system commands based on environment variables. By manipulating these variables through crafted HTTP requests, an attacker can inject arbitrary commands into the execution flow. The lack of proper input validation allows the injected commands to be executed with the router's privileges.

🙌 Credit to Researcher(s)

The vulnerability was reported by researchers at bananashipsBBQ.

🔗 References

🧵 Tags

#CVE-2025-7836 #D-Link #DIR-816L #CommandInjection #RCE #RouterSecurity #Vulnerability #Exploit

Summary: A critical command injection vulnerability exists in D-Link DIR-816L routers, allowing remote attackers with low privileges to execute arbitrary commands. Due to the device being end-of-life, patching is unlikely, and users should replace the device or take steps to mitigate the risk.

CVE ID: CVE-2025-7836

Risk Analysis: Successful exploitation allows an attacker to gain unauthorized access to the router, potentially changing DNS settings, installing malware, or using the router as a botnet node. This can lead to data theft, service disruption, and further compromise of the network.

Recommendation: Replace the D-Link DIR-816L with a supported router. If replacement is not possible, disable remote management, use a strong password, and isolate the router on a separate network segment.

Timeline

2025-07-19: CVE ID assigned and vulnerability reported.
2025-07-19: Public disclosure of the exploit.

CVE-2025-7836: D-Link DIR-816L Router Vulnerable to Remote Command Injection