CVE-2026-76651: TL-WR841N Buffer Overflow Vulnerability

CVE-2026-76651 Overview

CVE-2026-76651 is a buffer overflow vulnerability [CWE-120] in the embedded HTTP service of the TP-Link TL-WR841N v14 router. The flaw resides in the router's handling of multipart/form-data requests. Insufficient validation of the attacker-controlled boundary parameter allows a remote unauthenticated attacker on an adjacent network to submit a crafted request that overwrites memory beyond an internal buffer. Successful exploitation may corrupt process memory and cause undefined application behavior. Arbitrary code execution, information disclosure, and denial-of-service outcomes have not been demonstrated by the researcher or vendor.

Critical Impact
A remote unauthenticated attacker within adjacent network range can corrupt router process memory by sending a crafted multipart HTTP request with a malformed boundary parameter.

Affected Products

TP-Link TL-WR841N v14 router
Embedded HTTP administration service on the device
Firmware versions distributed via the TP-Link TL-WR841N v14 firmware download portal

Discovery Timeline

2026-08-28 - CVE-2026-76651 published to the National Vulnerability Database (NVD)
2026-09-01 - Last updated in the NVD database

Technical Details for CVE-2026-76651

Vulnerability Analysis

The vulnerability affects the embedded HTTP service that serves the router's administrative interface. When a client submits a request with a Content-Type: multipart/form-data header, the HTTP service parses the boundary parameter to delimit form segments. The parser does not adequately validate the length or structure of this attacker-controlled value before copying it into an internal buffer. A sufficiently long or malformed boundary value overflows the destination buffer and overwrites adjacent memory in the HTTP service process.

Because the affected endpoint is reachable without authentication and the attack vector is adjacent network, an attacker sharing the wireless or wired LAN segment can trigger the condition directly. The vendor has confirmed memory corruption but has not confirmed control-flow hijacking or reliable secondary impact.

Root Cause

The root cause is missing bounds checking on the boundary parameter of the Content-Type header during multipart request parsing. The classic buffer overflow pattern [CWE-120] results from a copy operation that trusts attacker-supplied length data without enforcing the fixed capacity of the destination buffer.

Attack Vector

An attacker with adjacent-network access to the router sends a single crafted HTTP request to the administration service. The request carries a Content-Type: multipart/form-data; boundary=<oversized_value> header. No authentication and no user interaction are required. Refer to the TP-Link TL-WR841N Firmware Download portal and the TP-Link TL-WR841N FAQ for vendor-supplied technical background. A verified public proof-of-concept is not currently available.

Detection Methods for CVE-2026-76651

Indicators of Compromise

HTTP requests to the router administration interface containing abnormally long boundary= values in the Content-Type header.
Unexpected restarts, watchdog resets, or service crashes of the router's embedded HTTP daemon.
Requests to /cgi-bin/ or administrative endpoints on port 80 or 443 from unauthenticated LAN hosts submitting multipart payloads.

Detection Strategies

Inspect wired and wireless LAN traffic for HTTP requests where the boundary parameter exceeds a reasonable length threshold, for example greater than 200 bytes.
Correlate router log entries showing HTTP service faults or restarts with preceding multipart POST requests from local hosts.
Alert on repeated malformed Content-Type headers directed at the router management IP.

Monitoring Recommendations

Enable and forward router syslog output to a central log store, and monitor for HTTP daemon termination or reboot events.
Restrict and audit LAN-side access to the router management interface, treating unexpected administrative traffic as suspicious.
Track EPSS scoring for CVE-2026-76651, currently 0.296% (percentile 21.809 as of 2026-09-03), for shifts that may indicate emerging exploitation activity.

How to Mitigate CVE-2026-76651

Immediate Actions Required

Restrict administrative access to the TL-WR841N v14 web interface to a defined management VLAN or trusted host list.
Disable remote (WAN-side) management if enabled, ensuring the HTTP service is not reachable outside the local subnet.
Inventory TL-WR841N v14 devices across the environment and prioritize firmware updates on those in high-traffic or guest network segments.

Patch Information

Check the TP-Link TL-WR841N v14 Firmware Download page for the latest firmware release addressing CVE-2026-76651. Apply the updated firmware following the procedure documented in the TP-Link TL-WR841N FAQ. Validate the firmware version after upgrade and reboot the device.

Workarounds

Segment the router management interface onto an isolated VLAN accessible only to administrators.
Enforce strong Wi-Fi authentication (WPA2/WPA3 with a long passphrase) to reduce the pool of adjacent-network attackers.
Where possible, place an upstream filtering device that drops HTTP requests with boundary parameters exceeding a defined length.

bash

# Example: block LAN clients from reaching the router admin interface
# except from a dedicated management host (run on an upstream firewall)
iptables -I FORWARD -d 192.168.0.1 -p tcp --dport 80 -j DROP
iptables -I FORWARD -s 192.168.0.10 -d 192.168.0.1 -p tcp --dport 80 -j ACCEPT