CVE-2026-5815: D-Link DIR-645 Buffer Overflow Vulnerability

CVE-2026-5815 Overview

CVE-2026-5815 is a stack-based buffer overflow vulnerability in the D-Link DIR-645 wireless router across firmware versions 1.01, 1.02, and 1.03. The flaw resides in the hedwigcgi_main function within /cgi-bin/hedwig.cgi. Attackers can exploit the issue remotely over the network with low privileges and no user interaction. A public exploit exists, increasing the likelihood of opportunistic attacks against exposed devices. The affected DIR-645 line is end-of-life, and D-Link will not release a security patch.

Critical Impact
Remote attackers can trigger memory corruption in hedwig.cgi to compromise confidentiality, integrity, and availability of unsupported D-Link DIR-645 routers.

Affected Products

D-Link DIR-645 firmware version 1.01
D-Link DIR-645 firmware version 1.02
D-Link DIR-645 firmware version 1.03

Discovery Timeline

2026-04-09 - CVE-2026-5815 published to the National Vulnerability Database (NVD)
2026-04-27 - Last updated in NVD database

Technical Details for CVE-2026-5815

Vulnerability Analysis

The vulnerability is a stack-based buffer overflow [CWE-119] inside the hedwigcgi_main function of /cgi-bin/hedwig.cgi. The CGI binary processes HTTP requests handled by the router's web administration interface. When the function copies attacker-controlled input into a fixed-size stack buffer without enforcing length checks, adjacent stack memory is overwritten. Overwriting saved return addresses on a MIPS-based embedded device allows control of execution flow.

Successful exploitation yields code execution in the context of the web service, which typically runs with elevated privileges on consumer routers. Because the DIR-645 series is no longer supported by D-Link, no vendor fix is planned. A public proof-of-concept has been published, lowering the skill barrier for exploitation.

Root Cause

The root cause is missing bounds validation when hedwigcgi_main parses request data into a stack-allocated buffer. The function copies user-supplied bytes without enforcing the destination buffer size, a classic violation of safe string handling in C. This pattern is widespread in legacy SOHO router firmware and is tracked under [CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer].

Attack Vector

An attacker reaches the vulnerable endpoint over HTTP on the router's management interface. The exploit can be launched remotely when the management interface is exposed to untrusted networks. Authentication is required at a low privilege level, but DIR-645 devices frequently retain default credentials, which weakens this prerequisite in practice. Detailed exploitation steps and a proof-of-concept are documented in the GitHub CVE Analysis and the VulDB #356263 entries.

No verified code examples are reproduced here. Refer to the linked advisory for technical details on crafting the overflow payload.

Detection Methods for CVE-2026-5815

Indicators of Compromise

Unexpected HTTP POST or GET requests targeting /cgi-bin/hedwig.cgi from unfamiliar source IP addresses.
Router crashes, reboots, or watchdog resets coinciding with inbound HTTP traffic to the management interface.
New outbound connections from the router to attacker-controlled infrastructure, indicating post-exploitation command-and-control.
Modified DNS settings on the device or unexpected firmware behavior after suspicious web requests.

Detection Strategies

Monitor network traffic for HTTP requests to hedwig.cgi originating outside trusted management subnets.
Inspect request bodies for abnormally long parameter values consistent with buffer overflow payloads.
Correlate router syslog events with NetFlow data to identify exploitation attempts followed by anomalous egress traffic.

Monitoring Recommendations

Forward router syslog and authentication logs to a centralized logging platform for retention and analysis.
Alert on any access to the router's management interface from WAN-side IP addresses.
Baseline normal administrative traffic patterns and flag deviations such as repeated CGI requests within short intervals.

How to Mitigate CVE-2026-5815

Immediate Actions Required

Replace D-Link DIR-645 devices with a currently supported router that receives security updates.
Disable remote management on the WAN interface until the device is decommissioned.
Restrict access to the LAN-side management interface using ACLs or a dedicated management VLAN.
Change default credentials and enforce strong administrator passwords on any remaining DIR-645 units.

Patch Information

No patch is available. D-Link has confirmed the DIR-645 product line is end-of-life and no longer maintained. The vendor recommendation is hardware replacement. Refer to the D-Link Security Information portal for end-of-life guidance.

Workarounds

Place the device behind an upstream firewall that blocks inbound traffic to TCP ports used by the web administration service.
Segment the router onto an isolated network with no access to sensitive internal assets.
Disable the HTTP administration interface where the firmware supports doing so, leaving only console or out-of-band access.

bash

# Example upstream firewall rule blocking external access to the router management port
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -i <wan_iface> -j DROP
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -i <wan_iface> -j DROP