CVE-2026-9105: TP-Link TL-WR841N Firmware DoS Vulnerability

CVE-2026-9105 Overview

CVE-2026-9105 is an authenticated stack-based buffer overflow in the web management interface of the TP-Link TL-WR841N v14 wireless router. An attacker with valid administrative credentials can send crafted HTTP requests to the embedded web server, overflowing a fixed-size stack buffer. Successful exploitation crashes the affected process and forces the device into an automatic reboot cycle, producing a denial-of-service condition on the network segment. The weakness is tracked under [CWE-121] (Stack-Based Buffer Overflow) and [CWE-787] (Out-of-Bounds Write). The vulnerability requires adjacent-network access, meaning the attacker must reach the router's LAN or wireless management interface.

Critical Impact
Authenticated attackers on the adjacent network can trigger a persistent crash-and-reboot loop on the TL-WR841N v14, disrupting wireless and wired connectivity for all downstream clients.

Affected Products

TP-Link TL-WR841N hardware revision v14
TP-Link TL-WR841N firmware (all versions prior to the vendor fix)
Deployments exposing the web management interface to LAN or Wi-Fi clients

Discovery Timeline

2026-06-29 - CVE-2026-9105 published to the National Vulnerability Database
2026-07-01 - Last updated in NVD database

Technical Details for CVE-2026-9105

Vulnerability Analysis

The TL-WR841N v14 exposes an embedded HTTP server for device administration. One or more request handlers copy attacker-controlled data from HTTP request fields into a fixed-size stack buffer without enforcing length validation. When the input exceeds the destination buffer's capacity, adjacent stack memory is overwritten, corrupting saved registers and the return address. The resulting invalid control flow terminates the web server process and triggers the watchdog-driven reboot behavior common to consumer-grade SOHO routers.

Exploitation requires prior authentication, so the attacker must already hold administrator credentials or must have compromised them through other means such as default credentials, credential reuse, or phishing. The impact is limited to availability. The CVE record does not indicate that the flaw yields code execution, and no public proof-of-concept or in-the-wild exploitation has been reported.

Root Cause

The root cause is a missing or insufficient bounds check on user-supplied HTTP parameters processed by the web management daemon. The handler uses an unsafe copy operation into a stack-allocated buffer, so oversized input writes past the buffer boundary. This maps directly to [CWE-121] and [CWE-787].

Attack Vector

The attack vector is adjacent network. The attacker must be able to reach the router's HTTP administration port, typically from the LAN or associated Wi-Fi network, and must present valid administrator credentials. The attacker then issues crafted HTTP requests containing oversized field values. Each request crashes the web server and initiates a reboot, and repeated requests sustain the denial-of-service condition. The device does not expose this interface to the WAN by default, which constrains remote reachability.

No verified exploit code is publicly available. Technical details are described in prose here; see the TP-Link vendor advisory for firmware-specific remediation guidance.

Detection Methods for CVE-2026-9105

Indicators of Compromise

Repeated unscheduled reboots of the TL-WR841N v14, visible as gaps in DHCP lease renewals and gateway ARP entries
System log entries indicating web management daemon crashes or watchdog-initiated restarts
Bursts of oversized or malformed HTTP POST requests directed at the router's administrative IP address from a LAN or wireless host

Detection Strategies

Monitor the router's syslog output, forwarded to a central collector, for repeated process crashes and reboot events on the web management service
Inspect LAN traffic for HTTP requests to the router management interface that carry abnormally long parameter values or headers
Correlate loss of gateway reachability with authenticated administrative sessions to identify the source host

Monitoring Recommendations

Forward router syslog to a centralized logging platform and alert on reboot frequency exceeding a baseline
Restrict which internal hosts can reach the router management interface and log all connections to that address and port
Track administrative login events and correlate them with subsequent device availability changes

How to Mitigate CVE-2026-9105

Immediate Actions Required

Apply the latest TL-WR841N v14 firmware from the TP-Link firmware download page as soon as it addresses this issue
Rotate the router administrator password and remove any shared or default credentials
Disable remote management and confirm the web interface is not reachable from the WAN
Segment management access so only a defined admin workstation or VLAN can reach the router's HTTP interface

Patch Information

TP-Link publishes firmware updates for the TL-WR841N v14 on its regional support portals. Refer to the TP-Link FAQ on TL-WR841N and the firmware download pages for the US region and the international region. Verify the firmware image checksum before flashing and confirm the hardware revision printed on the device label matches v14.

Workarounds

Restrict access to the web management interface using LAN-side ACLs or by placing the router management address on an isolated VLAN
Enforce strong, unique administrator credentials and remove unused administrative accounts
Disable Wi-Fi-side administrative access so that only wired hosts on the trusted segment can reach the management UI
Consider replacing end-of-support units with a currently maintained model if no fixed firmware is available for the deployed revision

bash

# Example: block LAN clients other than the admin workstation from reaching the router management IP
# Run on an upstream L3 switch or firewall protecting the router segment
iptables -A FORWARD -s 192.0.2.10/32 -d 192.168.0.1 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d 192.168.0.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.0.1 -p tcp --dport 443 -j DROP