CVE-2026-7853: D-Link DI-8100 Buffer Overflow Vulnerability

CVE-2026-7853 Overview

CVE-2026-7853 is a remotely exploitable buffer overflow in the D-Link DI-8100 router running firmware version 16.07.26A1. The flaw resides in the HTTP handler that processes requests to /auto_reboot.asp, where a sprintf call writes the enable and time arguments into a fixed-size buffer without bounds checking. An unauthenticated network attacker can supply oversized values to corrupt adjacent memory on the device. A public proof-of-concept has been released, increasing the likelihood of opportunistic exploitation against exposed devices. The weakness is classified under CWE-119 — improper restriction of operations within the bounds of a memory buffer.

Critical Impact

Unauthenticated remote attackers can trigger a buffer overflow in the DI-8100 HTTP service, leading to denial of service or potential code execution on the router.

Affected Products

• D-Link DI-8100 router (hardware)
• D-Link DI-8100 firmware version 16.07.26A1
• Networks exposing the DI-8100 web management interface to untrusted networks

Discovery Timeline

• 2026-05-05 - CVE-2026-7853 published to NVD
• 2026-05-06 - Last updated in NVD database

Technical Details for CVE-2026-7853

Vulnerability Analysis

The vulnerability lives in the request handler for /auto_reboot.asp, a web endpoint used to schedule automatic reboots on the DI-8100. The handler reads the enable and time parameters from the HTTP request and passes them to sprintf to build a configuration string. Because sprintf performs no length validation, attacker-controlled input can exceed the destination buffer and overwrite adjacent stack or heap data. The result is memory corruption inside the embedded HTTP daemon, classified under [CWE-119]. Successful exploitation can crash the daemon or, with a crafted payload, redirect execution to attacker-controlled instructions.

Root Cause

The root cause is the use of unbounded string formatting. The handler trusts user-supplied query or POST parameters and concatenates them into a fixed-size buffer through sprintf instead of using bounded equivalents such as snprintf. No input length validation is performed before the call, and no canary or stack protection appears to mitigate corruption on the affected firmware build.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker only needs HTTP reachability to the management interface. Devices with the web UI exposed to the WAN, or attackers already on the LAN, can issue a single crafted request to /auto_reboot.asp with oversized enable or time arguments to trigger the overflow. Technical details and reproduction steps are documented in the public GitHub PoC repository and tracked in VulDB #361130.

Detection Methods for CVE-2026-7853

Indicators of Compromise

• HTTP requests to /auto_reboot.asp containing abnormally long enable or time parameter values.
• Repeated reboots or crashes of the DI-8100 HTTP management daemon without administrator action.
• Unexpected configuration changes or new administrative sessions following reboot events.
• Inbound traffic to the router management interface from untrusted source addresses.

Detection Strategies

• Inspect web access and firewall logs for POST or GET requests targeting /auto_reboot.asp with parameter lengths exceeding normal client behavior.
• Deploy network IDS signatures that flag oversized enable= or time= values destined for DI-8100 management ports.
• Correlate router crash or reboot events with preceding HTTP requests to identify exploitation attempts.

Monitoring Recommendations

• Forward router syslog and HTTP server logs to a centralized logging or SIEM platform for retention and alerting.
• Alert on any management-plane HTTP traffic originating outside approved administrator subnets.
• Track device availability metrics to surface repeated daemon crashes consistent with overflow probing.

How to Mitigate CVE-2026-7853

Immediate Actions Required

• Restrict access to the DI-8100 web management interface to trusted administrative networks only and disable WAN-side management.
• Place the device behind a perimeter firewall and block inbound HTTP/HTTPS to the router from untrusted sources.
• Audit current firmware on all DI-8100 units and inventory any device running 16.07.26A1.
• Monitor D-Link Security Resources for an official advisory and firmware update addressing this issue.

Patch Information

At the time of publication, no vendor patch is referenced in the NVD entry for CVE-2026-7853. Administrators should consult D-Link Security Resources and the VulDB advisory for updated firmware availability. Until a fixed firmware build is released, network-level mitigations are the primary defense.

Workarounds

• Disable remote (WAN) administration on the DI-8100 and require management access only over a dedicated VLAN or VPN.
• Apply ACLs on upstream firewalls to permit management HTTP traffic only from specific administrator IP addresses.
• Replace end-of-life or unsupported DI-8100 units with currently supported router models if no firmware fix becomes available.
• Schedule regular configuration backups so devices can be restored quickly after a crash or compromise.