CVE-2025-13550: D-Link DIR-822K Buffer Overflow Flaw

CVE-2025-13550 Overview

CVE-2025-13550 is a buffer overflow vulnerability affecting D-Link DIR-822K and DWR-M920 routers. The flaw resides in an unknown function within the /boafrm/formVpnConfigSetup endpoint of the embedded web server. Attackers can trigger the condition by manipulating the submit-url argument, causing memory corruption on the device. The vulnerability is remotely exploitable and requires only low-privilege access. Public disclosure of exploitation details has occurred, increasing the likelihood of opportunistic attacks against exposed devices. The defect is classified under [CWE-119], improper restriction of operations within the bounds of a memory buffer.

Critical Impact
Remote attackers with low privileges can corrupt memory on affected D-Link routers through the VPN configuration handler, potentially leading to denial of service or arbitrary code execution on the device.

Affected Products

D-Link DIR-822K firmware 1.00_20250513164613
D-Link DWR-M920 firmware 1.1.50 (hardware revision B2)
D-Link DIR-822K and DWR-M920 hardware platforms running the affected firmware

Discovery Timeline

2025-11-23 - CVE-2025-13550 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-13550

Vulnerability Analysis

The vulnerability exists in the boa web server component of the affected D-Link routers, specifically in the handler bound to /boafrm/formVpnConfigSetup. This handler processes VPN configuration submissions from the device administration interface. When the handler parses the submit-url parameter from the HTTP request, it copies the supplied value into a fixed-size buffer without enforcing proper length validation. Supplying an oversized submit-url argument overflows adjacent memory regions on the device. Because embedded MIPS or ARM Linux firmware of this class typically lacks modern exploit mitigations such as stack canaries or address space layout randomization, memory corruption commonly translates into reliable control-flow hijacking.

Root Cause

The root cause is missing bounds checking on user-controlled input prior to a memory copy operation. The boa server's request parser places attacker-controlled query or POST data into a stack-allocated buffer using an unsafe string operation. This is a textbook [CWE-119] flaw, consistent with prior buffer overflow patterns reported in D-Link formXxx handlers.

Attack Vector

An authenticated attacker with low privileges sends a crafted HTTP request to the /boafrm/formVpnConfigSetup endpoint. The request includes an excessively long submit-url parameter. Processing the request triggers the overflow inside the web server process, which typically runs with root privileges on consumer router firmware. The attack is network-reachable and does not require user interaction. Exploitation details have been publicly disclosed via GitHub CVE Issue #33 and GitHub CVE Issue #47.

No verified proof-of-concept code is reproduced here. Refer to the VulDB entry #333317 for additional technical detail on the overflow primitive and the exact request structure required to reach the vulnerable path.

Detection Methods for CVE-2025-13550

Indicators of Compromise

HTTP requests to /boafrm/formVpnConfigSetup containing abnormally long values in the submit-url parameter.
Unexpected reboots, crashes, or watchdog-triggered restarts of the router web management process.
Outbound connections from the router to unfamiliar hosts following administrative interface access.
New or modified VPN configuration entries that do not correspond to authorized administrative activity.

Detection Strategies

Inspect web server access logs for POST requests to /boafrm/formVpnConfigSetup with submit-url payloads exceeding expected length thresholds.
Deploy network intrusion detection signatures matching oversized parameter values directed at D-Link boafrm endpoints.
Monitor authentication events on the router administrative interface for low-privilege accounts initiating VPN configuration changes.

Monitoring Recommendations

Restrict and log management plane access to the router from internal trusted networks only.
Forward router syslog and web access events to a centralized logging platform for retention and correlation.
Alert on repeated failed or malformed requests against /boafrm/ URIs, which often precede exploitation attempts.

How to Mitigate CVE-2025-13550

Immediate Actions Required

Disable remote (WAN-side) access to the router administrative web interface until a fix is available.
Limit LAN-side access to the management interface to a dedicated administrative VLAN or specific source IP addresses.
Rotate administrative credentials and remove unused low-privilege accounts that could be leveraged to reach the vulnerable endpoint.
Audit existing VPN configuration entries for unauthorized changes.

Patch Information

At the time of publication, no vendor patch has been referenced in the CVE record. Monitor the D-Link security advisory portal for firmware updates addressing the DIR-822K and DWR-M920 platforms. Apply firmware updates promptly once released, and validate the firmware image signature before deployment.

Workarounds

Block external access to TCP ports used by the router web management interface at the upstream firewall.
Enforce HTTPS-only management and disable HTTP where supported, reducing exposure of the vulnerable handler.
Replace end-of-life or unsupported D-Link models with vendor-supported alternatives where a patch is not forthcoming.
Segment IoT and network infrastructure devices from user and server networks to limit lateral movement if a device is compromised.

bash

# Example: restrict management interface access using an 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 443 -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 -j DROP