CVE-2026-7851: Dlink DI-8100 Buffer Overflow Vulnerability

CVE-2026-7851 Overview

CVE-2026-7851 is a stack-based buffer overflow vulnerability in the D-Link DI-8100 router running firmware version 16.07.26A1. The flaw resides in the sprintf function call within the yyxz.asp file, where the ID parameter is processed without proper bounds checking. Attackers can manipulate the ID argument remotely to overflow the stack buffer, potentially leading to memory corruption and arbitrary code execution on the affected device. The vulnerability is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer) and affects networked deployments where the device's web interface is reachable.

Critical Impact

Remote attackers with valid credentials can trigger a stack-based buffer overflow in the D-Link DI-8100 web interface, compromising confidentiality, integrity, and availability of the device.

Affected Products

• D-Link DI-8100 (hardware)
• D-Link DI-8100 Firmware version 16.07.26A1
• Network deployments exposing the yyxz.asp endpoint

Discovery Timeline

• 2026-05-05 - CVE-2026-7851 published to the National Vulnerability Database (NVD)
• 2026-05-06 - Last updated in NVD database

Technical Details for CVE-2026-7851

Vulnerability Analysis

The vulnerability stems from unsafe use of the sprintf function in the yyxz.asp handler on the D-Link DI-8100 router. The sprintf call writes formatted data into a fixed-size stack buffer using attacker-controlled input from the ID HTTP parameter. Because the function does not validate or constrain the length of the ID value before writing, oversized input overruns the stack buffer and corrupts adjacent memory, including saved return addresses and frame pointers.

This class of memory corruption flaw, [CWE-119], commonly enables attackers to redirect execution flow on embedded MIPS or ARM-based router firmware. Successful exploitation against the DI-8100 can yield arbitrary code execution within the context of the web server process, which typically runs with elevated privileges on consumer and small-business routers. Refer to the GitHub Report on Overflow for the published technical analysis.

Root Cause

The root cause is the absence of length validation on the ID request parameter before it is concatenated into a stack-allocated buffer through sprintf. The function lacks a bounds-aware variant such as snprintf, allowing input of arbitrary length to corrupt the stack frame.

Attack Vector

The attack is delivered over the network against the device's HTTP management interface. An authenticated attacker submits a crafted request to yyxz.asp with an oversized ID parameter. According to public reporting, exploit details are available, increasing the likelihood of opportunistic exploitation against exposed devices. See the VulDB #361128 entry for additional context.

No verified exploit code examples are reproduced here. Consult the VulDB #361128 CTI and GitHub Report on Overflow for technical details.

Detection Methods for CVE-2026-7851

Indicators of Compromise

• HTTP requests to /yyxz.asp containing an unusually long ID parameter value
• Unexpected reboots, watchdog resets, or web server crashes on DI-8100 devices
• Outbound connections from the router to unfamiliar hosts following suspicious HTTP traffic
• Modified firmware checksums or unauthorized configuration changes on the device

Detection Strategies

• Inspect HTTP request logs for ID parameter values exceeding expected lengths sent to yyxz.asp
• Deploy network signatures on perimeter IDS/IPS to flag oversized query strings targeting D-Link administrative endpoints
• Correlate router crash events with preceding HTTP traffic patterns to identify exploitation attempts
• Monitor authentication logs for credential reuse or brute-force activity preceding overflow attempts

Monitoring Recommendations

• Forward router syslog and HTTP access logs to a centralized SIEM for retention and correlation
• Alert on access to administrative interfaces from non-management network segments
• Track firmware version inventory across deployed D-Link devices to identify unpatched assets
• Enable behavioral monitoring on networks where DI-8100 devices are deployed to detect post-exploitation activity

How to Mitigate CVE-2026-7851

Immediate Actions Required

• Restrict access to the DI-8100 web management interface to trusted management VLANs only
• Disable remote (WAN-side) administration on all DI-8100 devices until a patch is applied
• Rotate administrative credentials, since exploitation requires authenticated access
• Inventory all DI-8100 units running firmware 16.07.26A1 and prioritize them for remediation

Patch Information

At the time of publication, no vendor advisory or fixed firmware release has been linked in the CVE record. Monitor the D-Link Official Website and the VulDB Submission #807798 entry for updates regarding a patched firmware build.

Workarounds

• Place DI-8100 devices behind a network firewall that blocks inbound HTTP/HTTPS to the management port from untrusted networks
• Enforce strong, unique administrative passwords and enable account lockout where supported
• Use a VPN or jump host for any required remote administration of the device
• Consider replacing the device with a supported model if a vendor patch is not released in a timely manner

# Example: restrict access to DI-8100 management interface using an upstream firewall
iptables -A FORWARD -p tcp -d <DI-8100-IP> --dport 80 -s <MGMT-SUBNET> -j ACCEPT
iptables -A FORWARD -p tcp -d <DI-8100-IP> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <DI-8100-IP> --dport 443 -s <MGMT-SUBNET> -j ACCEPT
iptables -A FORWARD -p tcp -d <DI-8100-IP> --dport 443 -j DROP