demining/bluetooth-attacks-cve-2025-27840Bitcoin Cryptanalysis: CVE-2025-27840 Vulnerability in ESP32 Microcontrollers Puts Billions of IoT Devices at Risk via Wi-Fi & Bluetooth
This paper discusses how an attacker can introduce a hidden list of vulnerabilities through module updates, which can lead to compromise of ESP32 devices and gaining unauthorized access to private keys, affecting billions of devices using this microcontroller. One of the key issues is the CVE-2025-27840 vulnerability discovered in the ESP32 architecture. To ensure security for the Bitcoin network, we identified the following vulnerabilities, where the possibility of using invalid private keys due to the lack of a lower bound check in the function has_invalid_privkey; a vulnerability in the transaction signature forgery in the function electrum_sig_hash due to incompatibility with BIP-137; a weak PRNG issue in the key generation function random_key, making personal private keys for cryptocurrency wallets predictable; lack of verification of points on the ECC curve in the function multiply, which can lead to invalid curve attacks; a vulnerability in the function ecdsa_raw_sign when restoring the Y-coordinate, potentially leading to a substitution of the public key; and vulnerabilities related to deprecated hashing APIs in the bin_ripemd160.
In early March 2025, Tarlogic Security identified a vulnerability in the ESP32 microcontroller, which is widely used to connect devices via WiFi and Bluetooth. This vulnerability was filed under the number CVE-2025-27840 . Attackers can unauthorizedly access Bitcoin wallet data by using the ESP32 chip as a point for cryptographic attacks on devices running on the networks of popular cryptocurrencies such as Bitcoin and Ethereum. This issue affects millions of IoT devices that use this microcontroller. Exploiting this vulnerability will allow attackers to carry out attacks disguised as legitimate users and permanently infect vulnerable devices. This threatens the security of IoT devices based on the ESP32 microcontroller and can lead to the theft of private keys of Bitcoin wallets.
ESP32 is a microcontroller that is widely used in IoT devices to provide Wi-Fi and Bluetooth connectivity. Attackers can use various methods to gain access to the private key data of Bitcoin wallets through ESP32.
Security threats related to the ESP32 microcontroller can lead to the theft of private keys of Bitcoin wallets. The main problems include the presence of backdoors and vulnerabilities. Using such vulnerabilities, they can manipulate memory, spoof MAC addresses, and inject malicious code, which creates serious security risks.
Attackers can attack IoT devices with an ESP32 microcontroller using vulnerabilities in Bluetooth and Wi-Fi connections, which can become a tool for attacking other devices on the Bitcoin-related network, as well as stealing confidential information, including private keys for Bitcoin wallets.
An attacker can update modules and introduce a list of various vulnerabilities into the code, including:
has_invalid_privkeythat can be used to obtain the private key.electrum_sig_hashallows forging Bitcoin transaction signatures.random_keyrelated to a weak pseudo-random number generator (non-deterministic PRNG).multiplywhere there is no check of a point on the ECC curve.ecdsa_raw_sign and bin_ripemd160.These vulnerabilities can be used to inject fake updates into ESP32 devices, giving attackers low-level access to the system. This will allow them to bypass code audit controls and gain access to private keys. Currently, billions of devices may be vulnerable due to hidden features of a single component in their architecture, which is designated as CVE-2025-27840.
has_invalid_privkeyThis vulnerability was found in Bitcoin’s private key verification code, allowing invalid keys (less than or equal to 0) to be used due to the lack of a lower bound check. This can lead to loss of funds. To fix this, a check must be added to ensure that the private key is greater than 0. The code is provided for demonstration purposes.
