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CVE-2026-36606.md

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CVE-2026-36606: Hardcoded DES Key for Configuration Backup Encryption

MITRE Description

Mercusys AC12G (EU) V1 router with firmware AC12G(EU)_V1_200909 encrypts configuration backups with a hardcoded DES key using single DES in ECB mode. An attacker who obtains a backup file can decrypt it to recover all stored credentials including admin password, WiFi PSK, and DDNS credentials.

Details

The configuration backup feature encrypts backups using a hardcoded DES key (0x478DA50BF9E3D2CF) in ECB mode with a 16-byte header (SDMP_CONF_V004). The firmware calls DES_set_key_unchecked (no key validation) and uses single DES with 56-bit effective key strength.

The encryption pipeline is:

Config TLV data -> Proprietary TP-Link LZ compression -> DES-ECB encryption -> SDMP_CONF_V004 header

Decryption requires skipping the 16-byte header and applying DES-ECB decryption with the known key.

Once decrypted, the configuration contains all device credentials in plaintext:

  • Admin password
  • WiFi WPA2 pre-shared keys (both 2.4GHz and 5GHz)
  • PPPoE username and password
  • DDNS credentials
  • Guest network credentials

This same DES key is shared across multiple TP-Link and Mercusys firmware versions and is publicly documented in router security research.

Severity

High

CVSS v3.1

Score: 7.4
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CWE

  • CWE-321: Use of Hard-Coded Cryptographic Key
  • CWE-798: Use of Hard-Coded Credentials

Affected Product

Field Value
Vendor Mercusys (TP-Link sub-brand)
Product AC12G (EU) V1
Tested Firmware AC12G(EU)_V1_200909, AC12G(EU)_V1_210128
Component Configuration backup/restore functionality, encryption module
Status End-of-life (no fix planned)

Impact

  • Complete credential exposure if a configuration backup file is obtained by any means
  • DES is cryptographically broken - 56-bit effective key is brute-forceable
  • The same key is shared across TP-Link/Mercusys product lines
  • Config backup download requires authentication (code=4), but the encryption adds no real protection once a file is obtained

Remediation

  1. Use AES-256 with a device-unique key derived from hardware serial number
  2. Do not use hardcoded cryptographic keys shared across devices
  3. Use authenticated encryption (AES-GCM) instead of ECB mode

Discoverer

Tymbark7372

References