CVE-2020-26558 in Bluetooth
Summary
by MITRE • 05/25/2021
Bluetooth LE and BR/EDR secure pairing in Bluetooth Core Specification 2.1 through 5.2 may permit a nearby man-in-the-middle attacker to identify the Passkey used during pairing (in the Passkey authentication procedure) by reflection of the public key and the authentication evidence of the initiating device, potentially permitting this attacker to complete authenticated pairing with the responding device using the correct Passkey for the pairing session. The attack methodology determines the Passkey value one bit at a time.
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Analysis
by VulDB Data Team • 11/04/2025
This vulnerability affects Bluetooth implementations that adhere to the Bluetooth Core Specification versions 2.1 through 5.2, specifically targeting the secure pairing mechanisms designed to protect against unauthorized access during device establishment. The flaw exists in the Passkey authentication procedure where Bluetooth devices engage in a cryptographic exchange to verify their identities. When a nearby attacker can intercept and manipulate the public key exchange and authentication evidence transmitted between devices, they can exploit this weakness to determine the passkey value through a process called reflection attack. The vulnerability stems from insufficient validation of the cryptographic parameters exchanged during the pairing process, allowing an attacker to reverse-engineer the passkey bit by bit.
The technical implementation flaw manifests in how the Bluetooth stack handles the Diffie-Hellman key exchange and authentication verification steps during secure pairing. During the pairing process, devices exchange public keys and authentication evidence to establish a shared secret and verify identity. However, the vulnerability allows an attacker positioned within Bluetooth range to capture these exchanges and use mathematical reflection techniques to deduce the passkey. This attack operates at the protocol level rather than exploiting implementation bugs, making it particularly concerning as it affects the fundamental security model of Bluetooth pairing. The process of determining the passkey value occurs one bit at a time, requiring multiple iterations but ultimately enabling complete passkey recovery without requiring advanced cryptographic skills or significant computational resources.
The operational impact of this vulnerability extends beyond simple unauthorized device access, as it can enable attackers to establish persistent authenticated connections with target devices. An attacker who successfully determines the passkey can subsequently complete authenticated pairing sessions with devices, potentially gaining access to sensitive data, controlling device functions, or using the established trust relationship to launch further attacks. This vulnerability particularly affects devices that rely on passkey entry for pairing, such as smartphones, laptops, tablets, and IoT devices that require user interaction to complete Bluetooth pairing. The attack requires only proximity to the devices involved in the pairing process, making it feasible in public spaces, offices, or homes where Bluetooth devices are in use, with the attacker needing no specialized equipment beyond standard Bluetooth monitoring tools.
Mitigation strategies should focus on implementing stronger cryptographic validation mechanisms during the pairing process, including enhanced public key validation and authentication evidence verification. Device manufacturers should ensure their Bluetooth implementations properly validate all cryptographic parameters exchanged during secure pairing, particularly the Diffie-Hellman public key values and authentication signatures. The implementation should incorporate protections against reflection attacks by ensuring that public keys are properly validated and that authentication evidence cannot be manipulated to reveal passkey information. Organizations should consider implementing additional security controls such as device pinning, trusted device lists, and regular security audits of Bluetooth implementations. This vulnerability aligns with CWE-310, which addresses cryptographic weaknesses, and maps to ATT&CK technique T1565.001, which covers credential dumping and authentication bypass through protocol manipulation. Users should be educated about the risks of pairing devices in public spaces and the importance of verifying pairing requests before accepting them. The vulnerability demonstrates the critical importance of proper cryptographic protocol implementation and the need for thorough security testing of wireless communication protocols.