CVE-2021-4239 in noise
Summary
by MITRE • 12/28/2022
The Noise protocol implementation suffers from weakened cryptographic security after encrypting 2^64 messages, and a potential denial of service attack. After 2^64 (~18.4 quintillion) messages are encrypted with the Encrypt function, the nonce counter will wrap around, causing multiple messages to be encrypted with the same key and nonce. In a separate issue, the Decrypt function increments the nonce state even when it fails to decrypt a message. If an attacker can provide an invalid input to the Decrypt function, this will cause the nonce state to desynchronize between the peers, resulting in a failure to encrypt all subsequent messages.
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Analysis
by VulDB Data Team • 01/25/2023
The noise protocol implementation vulnerability identified as CVE-2021-4239 represents a critical cryptographic weakness that fundamentally undermines the security guarantees of the encryption mechanism. This vulnerability stems from the improper handling of nonce counters within the encryption and decryption functions, creating both cryptographic degradation and denial of service conditions that can be exploited by malicious actors. The core issue manifests when the encryption function processes approximately 18.4 quintillion messages, at which point the 64-bit nonce counter wraps around, leading to the reuse of cryptographic keys with identical nonces, a condition that completely compromises the confidentiality guarantees of the noise protocol.
The technical flaw in this vulnerability aligns with CWE-327, which addresses the use of weak cryptographic algorithms and improper implementation of cryptographic primitives. The nonce reuse vulnerability specifically demonstrates a failure in implementing proper counter management within the cryptographic protocol, where the 64-bit counter reaches its maximum value and wraps around to zero, causing identical key-nonce pairs to be used for encryption. This creates a scenario where an attacker can potentially recover plaintext information through cryptanalytic attacks that exploit the reuse of key-nonce combinations, fundamentally breaking the security model that the noise protocol is designed to provide. The vulnerability also corresponds to CWE-310, which covers cryptographic issues related to improper key management and nonce handling, as the protocol fails to properly manage the lifecycle of cryptographic parameters.
The operational impact of this vulnerability extends beyond simple cryptographic weakness to include potential denial of service conditions that can completely disrupt communication between peers. When an attacker supplies invalid input to the decryption function, the nonce state becomes desynchronized between communicating parties, causing subsequent encryption operations to fail completely. This behavior creates a cascading failure where legitimate communication becomes impossible, effectively rendering the protocol unusable for its intended purpose. The vulnerability creates a scenario where an attacker can initiate a denial of service attack by simply providing malformed data to the decryption function, causing the system to become permanently stuck in a state where no further encryption can occur. This makes the vulnerability particularly dangerous in production environments where continuous communication is required and where a single malicious actor can cause widespread service disruption.
From an adversarial perspective, this vulnerability maps directly to several ATT&CK techniques including T1595 for cryptographic key compromise and T1499 for network denial of service attacks. The attack surface is particularly concerning because it can be exploited without requiring elevated privileges, making it accessible to any attacker who can establish communication with the vulnerable system. The vulnerability also demonstrates a lack of proper error handling and state management, which aligns with ATT&CK technique T1070 for indicator removal and T1566 for malicious code injection, as the improper handling of decryption failures creates opportunities for further exploitation. The fact that this vulnerability affects the fundamental cryptographic operations means that any system using the noise protocol implementation is at risk of both data compromise and service disruption.
The recommended mitigations for this vulnerability include implementing proper nonce management that prevents counter wrapping, adding validation checks to ensure that nonce states remain synchronized between peers, and implementing automatic rekeying mechanisms that prevent the use of the same key-nonce pair beyond safe limits. Organizations should also implement monitoring for unusual nonce behavior and establish proper error handling that does not modify state when decryption operations fail. The most effective immediate solution is to upgrade to a patched version of the noise protocol implementation that properly handles nonce wrapping and maintains synchronization between communicating parties, as the vulnerability cannot be adequately mitigated through configuration changes alone. Additionally, systems should be designed with proper cryptographic bounds checking and state validation to prevent similar issues from occurring in other cryptographic implementations.