CVE-2026-5040: TP-Link Deco M5 Information Disclosure

CVE-2026-5040 Overview

CVE-2026-5040 affects the TP-Link Deco M5 v1 mesh Wi-Fi system. The device stores user credentials using a weak password hashing mechanism, classified as [CWE-916] Use of Password Hash With Insufficient Computational Effort. An attacker who obtains the stored password hash through system compromise or privileged access can perform brute-force or dictionary attacks to recover plaintext credentials. Successful exploitation exposes authentication credentials and enables unauthorized access to device management functions. The primary security impact is loss of confidentiality of stored administrative credentials.

Critical Impact
Recovery of administrative credentials from weakly hashed storage permits full takeover of the Deco M5 mesh network, including DNS manipulation, traffic interception, and pivot into connected client devices.

Affected Products

TP-Link Deco M5 v1 mesh Wi-Fi system
Firmware versions prior to the fixed release published by TP-Link
Device management interfaces relying on the local credential store

Discovery Timeline

2026-07-14 - CVE-2026-5040 published to NVD
2026-07-15 - Last updated in NVD database

Technical Details for CVE-2026-5040

Vulnerability Analysis

The Deco M5 v1 firmware stores user credentials using a hashing algorithm that lacks sufficient computational cost. Modern password hashing requires adaptive functions such as bcrypt, scrypt, or Argon2, which include configurable work factors and per-user salts. Fast general-purpose hashes such as MD5 or SHA-1, or unsalted variants, allow adversaries to compute billions of candidate hashes per second on commodity GPUs.

An attacker with local access or a privileged foothold on the device can read the credential store and offload the recovered hashes for offline cracking. Because the router administrator password often controls the entire home or small-business network, recovering it grants control over DNS settings, firmware updates, and traffic routing.

Root Cause

The root cause is the selection of an inadequate password hashing primitive within the Deco M5 v1 authentication subsystem. The stored representation does not impose enough computational effort to resist offline brute-force or dictionary attacks. This weakness maps to [CWE-916] and reflects a design-time cryptographic choice rather than an implementation bug.

Attack Vector

The attack requires local access with high privileges, as reflected in the CVSS vector components AV:L and PR:H. An adversary first compromises the device or gains privileged shell access through another vulnerability, physical access, or credential reuse. The attacker then extracts the credential file and performs offline password recovery using tools such as Hashcat or John the Ripper. Once cleartext credentials are recovered, the attacker authenticates to the management interface and reconfigures the device.

No working exploit is publicly listed, and CISA KEV does not track CVE-2026-5040. However, the attack methodology is well-understood and repeatable against any device that exposes weak hashes to a local attacker.

Detection Methods for CVE-2026-5040

Indicators of Compromise

Unexpected administrative logins to the Deco M5 management interface from unfamiliar source addresses or client applications.
Unauthorized changes to DNS servers, port forwarding rules, or firmware update channels on the device.
Presence of shell access artifacts, debug interfaces, or unauthorized SSH sessions on the router.
New or modified administrative accounts appearing in the device configuration.

Detection Strategies

Monitor router configuration exports for drift against a known-good baseline, focusing on DNS, WAN, and access-control settings.
Alert on repeated failed authentications to the Deco management interface followed by a successful login from the same source.
Correlate outbound DNS traffic from client endpoints for redirection to attacker-controlled resolvers, which often follows router compromise.

Monitoring Recommendations

Ingest router syslog and administrative event logs into a centralized SIEM or data lake for retention and correlation.
Track firmware version reporting across the fleet to identify devices running vulnerable Deco M5 v1 builds.
Watch for lateral movement from network devices into endpoint estates, and use endpoint telemetry to identify credential reuse originating from router compromise.

How to Mitigate CVE-2026-5040

Immediate Actions Required

Apply the latest Deco M5 v1 firmware from the TP-Link support portal as soon as it is available for your region.
Rotate the Deco administrator password and any accounts that share the same credential across other systems.
Restrict management access to the Deco M5 to trusted local network segments and disable remote cloud management if not required.
Audit device configuration for unauthorized DNS servers, port forwards, or added administrative accounts.

Patch Information

TP-Link publishes firmware updates for the Deco M5 v1 on its regional support pages. Refer to the TP-Link Deco M5 Firmware download page for the current release and to TP-Link FAQ #5190 for firmware update procedures. Verify the installed version through the Deco mobile application after applying the update.

Workarounds

Segment the Deco M5 management network from untrusted hosts and IoT devices to reduce the likelihood of local privileged access.
Enforce strong, unique, high-entropy administrator passwords that resist dictionary attacks even against weak hashing.
Disable any exposed debug, SSH, or Telnet interfaces on the device and block them at upstream firewalls.
Replace end-of-life devices with hardware that implements modern password hashing primitives such as bcrypt or Argon2.

bash

# Configuration example: restrict management access at the upstream firewall
# Replace 192.0.2.10 with the trusted admin workstation and 198.51.100.1 with the Deco management IP
iptables -A FORWARD -s 192.0.2.10 -d 198.51.100.1 -p tcp --dport 443 -j ACCEPT
iptables -A FORWARD -d 198.51.100.1 -p tcp --dport 443 -j DROP
iptables -A FORWARD -d 198.51.100.1 -p tcp --dport 22 -j DROP
iptables -A FORWARD -d 198.51.100.1 -p tcp --dport 23 -j DROP