D-Link DI-8100 Remote Buffer Overflow Vulnerability (CVE-2026-7853)

A critical buffer overflow vulnerability, tracked as CVE-2026-7853, affects D-Link DI-8100 routers running firmware version 16.07.26A1. The vulnerability resides within the sprintf function of the /auto_reboot.asp file, which is part of the HTTP handler component. An attacker can exploit this flaw by crafting a malicious HTTP request with an overly long string in the enable/time argument. This causes a buffer overflow when the sprintf function attempts to write the data to a fixed-size buffer, potentially leading to arbitrary code execution on the device. The vulnerability is remotely exploitable and has a public exploit available, making it an attractive target for attackers. Successful exploitation allows attackers to gain control of the router, potentially enabling them to intercept network traffic, modify router settings, or use the device as a foothold for further attacks within the network.

Attack Chain

1. The attacker identifies a vulnerable D-Link DI-8100 router running firmware version 16.07.26A1.
2. The attacker crafts a malicious HTTP GET or POST request targeting the /auto_reboot.asp endpoint.
3. The crafted request includes the enable/time argument with a string exceeding the buffer’s capacity.
4. The router’s HTTP handler processes the request and passes the enable/time argument to the sprintf function.
5. sprintf attempts to write the oversized string into a fixed-size buffer, causing a buffer overflow.
6. The buffer overflow overwrites adjacent memory locations, potentially including the return address of the function.
7. Upon function return, the overwritten return address is used, redirecting execution to attacker-controlled code.
8. The attacker’s code executes with the privileges of the HTTP handler, potentially gaining complete control of the router.

Impact

Successful exploitation of CVE-2026-7853 allows a remote attacker to execute arbitrary code on the affected D-Link DI-8100 router. This can lead to a complete compromise of the device, enabling attackers to intercept network traffic, modify DNS settings, create VPN tunnels, or use the router as a botnet node. Given the availability of a public exploit, vulnerable routers are at high risk of being targeted in automated attacks.

Recommendation

• Apply available patches or firmware updates provided by D-Link to address CVE-2026-7853 when available.
• Monitor webserver logs for suspicious requests targeting the /auto_reboot.asp endpoint with unusually long enable/time parameters and deploy the Sigma rule “Detect CVE-2026-7853 Exploit Attempt via Long URI” to identify potential exploit attempts.
• Implement network intrusion detection systems (IDS) rules to detect and block malicious HTTP requests exploiting CVE-2026-7853.
• Disable remote administration access to the router to reduce the attack surface.