CVE-2026-4555: D-Link DIR-513 Buffer Overflow Vulnerability

CVE-2026-4555 Overview

A stack-based buffer overflow vulnerability has been identified in the D-Link DIR-513 router firmware version 1.10. The vulnerability exists in the formEasySetTimezone function within the /goform/formEasySetTimezone endpoint of the boa web server component. By manipulating the curTime argument, an attacker can trigger a stack-based buffer overflow condition, potentially leading to remote code execution or denial of service.

Critical Impact

This vulnerability affects an end-of-life product that is no longer supported by D-Link, meaning no official patches will be released. Attackers can remotely exploit this flaw to potentially gain control of affected devices or cause system crashes.

Affected Products

• D-Link DIR-513 firmware version 1.10
• D-Link DIR-513 devices running the boa web server component
• Products containing the vulnerable /goform/formEasySetTimezone endpoint

Discovery Timeline

• 2026-03-22 - CVE-2026-4555 published to NVD
• 2026-03-23 - Last updated in NVD database

Technical Details for CVE-2026-4555

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The root cause lies in the formEasySetTimezone function's failure to properly validate the length of user-supplied input in the curTime parameter before copying it to a fixed-size stack buffer.

When processing timezone configuration requests through the boa web server, the function accepts the curTime argument without adequate bounds checking. An attacker with network access and low-level authentication can send a specially crafted HTTP request to the /goform/formEasySetTimezone endpoint containing an oversized curTime value. This causes the input data to exceed the allocated stack buffer, overwriting adjacent memory including potentially the return address.

The exploitation of this vulnerability can result in arbitrary code execution with the privileges of the boa web server process, typically running with elevated permissions on embedded devices. Given the network-accessible nature of this attack vector and the low complexity required for exploitation, affected devices are at significant risk.

Root Cause

The vulnerability stems from improper input validation in the formEasySetTimezone function. The function fails to verify that the length of the curTime parameter does not exceed the size of the destination stack buffer before performing the copy operation. This classic buffer overflow pattern is common in embedded device firmware where memory-safe programming practices may not be consistently applied.

Attack Vector

The attack can be executed remotely over the network. An attacker needs low-privilege authentication to access the vulnerable endpoint. The exploitation process involves:

1. The attacker identifies a D-Link DIR-513 device running firmware version 1.10 accessible on the network
2. A malicious HTTP request is crafted targeting the /goform/formEasySetTimezone endpoint
3. The curTime parameter is populated with data exceeding the expected buffer size, potentially including shellcode or ROP gadgets
4. Upon processing the request, the stack buffer overflows, corrupting the stack and potentially hijacking program execution flow

The vulnerability has been publicly documented and exploit information is available, increasing the likelihood of attacks against unpatched devices.

Detection Methods for CVE-2026-4555

Indicators of Compromise

• Unusual HTTP POST requests to /goform/formEasySetTimezone endpoints with abnormally large curTime parameter values
• Unexpected crashes or restarts of the boa web server process on D-Link DIR-513 devices
• Network traffic containing potential shellcode patterns in requests to the vulnerable endpoint
• Anomalous outbound connections from the router following exploitation attempts

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests with oversized parameters targeting D-Link management interfaces
• Monitor for HTTP POST requests to /goform/formEasySetTimezone with curTime values exceeding normal timestamp lengths
• Deploy web application firewall rules to filter requests with suspicious payload sizes to goform endpoints
• Utilize network monitoring tools to detect potential command-and-control traffic originating from affected devices

Monitoring Recommendations

• Enable logging on upstream firewalls to capture all traffic to and from D-Link DIR-513 devices
• Implement network segmentation to isolate vulnerable end-of-life devices from critical network infrastructure
• Regularly review device access logs for unauthorized or suspicious administrative access attempts
• Consider deploying network traffic analysis tools to detect anomalous behavior patterns from embedded devices

How to Mitigate CVE-2026-4555

Immediate Actions Required

• Restrict network access to the D-Link DIR-513 management interface using firewall rules
• Consider replacing end-of-life D-Link DIR-513 devices with currently supported hardware
• Disable remote administration features if not required for operations
• Implement network segmentation to isolate affected devices from sensitive network segments
• Block external access to the vulnerable endpoint at the network perimeter

Patch Information

This vulnerability affects the D-Link DIR-513 which has reached end-of-life status and is no longer supported by the manufacturer. D-Link will not be releasing security patches for this vulnerability. Organizations using affected devices should prioritize replacement with supported alternatives.

For additional information, refer to the D-Link Security Homepage and the vulnerability documentation on VulDB.

Workarounds

• Implement access control lists (ACLs) on network equipment to restrict access to the router's management interface to trusted IP addresses only
• Deploy a network firewall or reverse proxy in front of the device to filter malicious requests targeting the /goform/formEasySetTimezone endpoint
• Disable the boa web server if the web management interface is not required for device operation
• Consider third-party firmware alternatives (such as OpenWrt, if compatible) that may address the vulnerability
• Schedule device replacement as the primary long-term mitigation strategy

# Example: Block access to vulnerable endpoint using iptables on upstream firewall
# Replace 192.168.1.1 with the actual IP of the D-Link DIR-513 device
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -m string --string "/goform/formEasySetTimezone" --algo bm -j DROP

# Restrict management interface access to trusted admin workstation only
iptables -A FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP