CVE-2026-7855: D-Link DI-8100 Buffer Overflow Vulnerability

CVE-2026-7855 Overview

CVE-2026-7855 is a buffer overflow vulnerability in the D-Link DI-8100 router running firmware version 16.07.26A1. The flaw resides in the tggl_asp function within the /tggl.asp file, which is part of the device's HTTP request handler. An attacker can manipulate the Name argument to trigger memory corruption. The vulnerability is classified under CWE-119, covering improper restriction of operations within the bounds of a memory buffer. Public exploit details are available, increasing the risk that adversaries weaponize this issue against exposed devices.

Critical Impact

Remote attackers with low privileges can exploit the buffer overflow over the network to compromise confidentiality, integrity, and availability of affected D-Link DI-8100 routers.

Affected Products

• D-Link DI-8100 (hardware)
• D-Link DI-8100 firmware version 16.07.26A1
• HTTP request handler component (/tggl.asp)

Discovery Timeline

• 2026-05-05 - CVE-2026-7855 published to NVD
• 2026-05-06 - Last updated in NVD database

Technical Details for CVE-2026-7855

Vulnerability Analysis

The vulnerability resides in the tggl_asp handler used by the DI-8100 web management interface. When the device processes an HTTP request directed at /tggl.asp, the handler reads the Name argument from user-supplied input. The handler fails to enforce proper boundary checks before copying the value into a fixed-size memory buffer. This results in a buffer overflow consistent with [CWE-119].

The flaw is reachable over the network and requires only low-level authentication to exploit. Successful exploitation can corrupt adjacent memory, alter program control flow, and lead to arbitrary code execution on the embedded Linux platform that powers the router. Public technical analysis of the issue is documented in the GitHub report on tggl.asp overflow and VulDB entry #361132.

Root Cause

The root cause is missing input length validation on the Name parameter. The web server copies attacker-controlled data into a stack or heap buffer without verifying that the source size fits the destination. Embedded HTTP daemons in consumer routers frequently rely on unsafe C string functions, and this case follows that pattern.

Attack Vector

An attacker sends a crafted HTTP request to /tggl.asp with an oversized Name argument. The request must reach the management interface, which means the attacker needs network access to the router and valid low-privileged credentials. Once the malformed request reaches the tggl_asp function, the overflow corrupts memory in the web service process. Public exploit material referenced by VulDB raises the likelihood of automated scanning and exploitation against exposed devices.

No verified proof-of-concept code is reproduced here. Refer to the GitHub report for technical details.

Detection Methods for CVE-2026-7855

Indicators of Compromise

• HTTP POST or GET requests to /tggl.asp containing abnormally long Name parameter values.
• Unexpected restarts or crashes of the router's web management daemon.
• New or unauthorized configuration changes on DI-8100 devices following inbound HTTP traffic.
• Outbound connections from the router to unknown external hosts after web interface activity.

Detection Strategies

• Inspect web server and router syslog data for repeated requests to /tggl.asp from a single source.
• Deploy network IDS signatures that flag HTTP requests where the Name parameter exceeds expected length thresholds.
• Correlate management interface access with off-hours activity or non-administrative source IP addresses.

Monitoring Recommendations

• Forward router logs to a central logging or SIEM platform for long-term retention and correlation.
• Monitor for repeated authentication failures followed by successful logins on the DI-8100 web UI.
• Track firmware version inventory across all D-Link devices to identify systems running 16.07.26A1.

How to Mitigate CVE-2026-7855

Immediate Actions Required

• Restrict access to the DI-8100 web management interface to trusted internal networks only.
• Disable remote (WAN-side) administration on affected routers.
• Rotate administrative credentials and remove unused low-privileged accounts that could be abused.
• Audit router logs for indicators consistent with the attack vector described above.

Patch Information

No vendor patch advisory is listed in the enriched CVE data at the time of publication. Monitor D-Link Security Information for firmware updates that supersede 16.07.26A1. Apply firmware updates as soon as the vendor releases a fixed version.

Workarounds

• Place affected DI-8100 devices behind a perimeter firewall that blocks untrusted access to TCP ports used by the web interface.
• Enforce network segmentation so management traffic to the router is only reachable from a dedicated administrative VLAN.
• Replace end-of-support DI-8100 units with currently supported router models if no firmware fix is available.

# Configuration example: restrict router management access via upstream firewall (iptables)
iptables -A FORWARD -p tcp -d <ROUTER_IP> --dport 80 -s <ADMIN_SUBNET> -j ACCEPT
iptables -A FORWARD -p tcp -d <ROUTER_IP> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <ROUTER_IP> --dport 443 -s <ADMIN_SUBNET> -j ACCEPT
iptables -A FORWARD -p tcp -d <ROUTER_IP> --dport 443 -j DROP