CVE-2025-3538: D-Link DI-8100 Buffer Overflow Vulnerability

CVE-2025-3538 Overview

CVE-2025-3538 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 auth_asp function within /auth.asp, served by the jhttpd component. Attackers manipulate the callback argument to corrupt the stack and trigger memory corruption. Exploitation requires adjacent network access, meaning the attacker must be present on the local network. The exploit has been publicly disclosed, increasing the risk of opportunistic attacks against exposed devices. The vulnerability maps to [CWE-119] (improper restriction of operations within memory buffer bounds) and [CWE-787] (out-of-bounds write).

Critical Impact
Adjacent network attackers can corrupt memory in jhttpd and potentially execute arbitrary code on affected D-Link DI-8100 routers, undermining the integrity, confidentiality, and availability of the device.

Affected Products

D-Link DI-8100 router (hardware)
D-Link DI-8100 firmware version 16.07.26A1
Deployments exposing the jhttpd web management service on the local network

Discovery Timeline

2025-04-13 - CVE-2025-3538 published to the National Vulnerability Database
2025-07-16 - Last updated in NVD database

Technical Details for CVE-2025-3538

Vulnerability Analysis

The defect lives in the auth_asp handler exposed by the embedded jhttpd web server on the DI-8100. The handler reads the callback query parameter from /auth.asp requests and copies it into a fixed-size stack buffer without enforcing length checks. A sufficiently long callback value overwrites adjacent stack memory, including saved registers and the return address. On MIPS-based D-Link routers, this class of bug commonly enables hijacking of control flow and execution of attacker-supplied shellcode. The flaw is reachable pre-authentication because auth.asp is invoked during the authentication workflow itself, exposing the entire LAN-facing attack surface. Public proof-of-concept material describing the issue is available in the GitHub PoC Repository.

Root Cause

The root cause is unbounded copying of attacker-controlled input into a stack buffer inside auth_asp. The function trusts the size of the callback parameter supplied in the HTTP request. Lack of bounds validation enables an out-of-bounds write on the stack, which is the underlying behavior captured by [CWE-787].

Attack Vector

Exploitation requires adjacent-network access, typically a foothold on the same LAN or Wi-Fi segment as the router. An attacker issues a crafted HTTP request to /auth.asp with an oversized callback parameter. No authentication or user interaction is required. The corrupted stack frame allows the attacker to redirect execution and run code in the context of jhttpd, which on these devices commonly runs with elevated privileges.

No verified exploit code is reproduced here. Refer to the GitHub PoC Repository and VulDB #304577 for technical details.

Detection Methods for CVE-2025-3538

Indicators of Compromise

HTTP requests to /auth.asp containing abnormally long callback query parameter values
Unexpected restarts or crashes of the jhttpd process on DI-8100 devices
Outbound connections from the router to unknown hosts following requests to /auth.asp
New or modified processes running with jhttpd parent context

Detection Strategies

Inspect web server and management interface logs for requests targeting /auth.asp with oversized parameters
Apply network intrusion detection signatures that flag callback parameter lengths exceeding expected bounds
Correlate LAN-side HTTP traffic to router management IPs with unusual response codes or connection resets
Baseline normal management traffic and alert on bursts of malformed requests from internal hosts

Monitoring Recommendations

Forward router syslog and HTTP access logs to a centralized logging platform for retention and analysis
Monitor for repeated authentication endpoint requests originating from unexpected internal hosts
Track firmware versions across the fleet to identify devices still running 16.07.26A1
Alert on configuration changes or new administrative sessions following anomalous /auth.asp activity

How to Mitigate CVE-2025-3538

Immediate Actions Required

Restrict access to the router management interface to a dedicated administrative VLAN or trusted host
Disable LAN-side HTTP management where remote configuration is not required
Segment guest and untrusted devices away from network segments that can reach the router web UI
Review router logs for indicators consistent with /auth.asp exploitation attempts

Patch Information

At the time of NVD publication, no vendor patch URL is referenced for CVE-2025-3538. Administrators should monitor the D-Link Security Resource for firmware updates superseding 16.07.26A1 and apply them as soon as they become available. Additional tracking information is available via VulDB CTI ID #304577.

Workarounds

Place the DI-8100 management interface behind ACLs that permit only specific administrator IP addresses
Disable the web management service on interfaces where it is not strictly required
Use 802.1X or strong WPA3 controls to limit which devices can join the adjacent network
Consider replacing end-of-support D-Link DI-8100 hardware if no firmware fix is released

bash

# Example ACL concept: limit management access to a single admin host
# (Apply the equivalent on the DI-8100 firewall/ACL configuration page)
allow tcp from 192.0.2.10 to <router_lan_ip> port 80
deny  tcp from any         to <router_lan_ip> port 80