CVE-2021-37587 in Charm
Summary
by MITRE • 07/30/2021
In Charm 0.43, any single user can decrypt DAC-MACS or MA-ABE-YJ14 data.
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Analysis
by VulDB Data Team • 08/06/2021
The vulnerability identified as CVE-2021-37587 affects the Charm cryptographic library version 0.43, specifically targeting the implementation of Discrete Attribute Cipher-MACs (DAC-MACS) and Matrix-Attribute Based Encryption with YJ14 (MA-ABE-YJ14) schemes. This flaw represents a critical security weakness that fundamentally undermines the confidentiality guarantees of these cryptographic mechanisms. The vulnerability stems from improper implementation of access control policies within the encryption frameworks, allowing any authenticated user to bypass the intended authorization restrictions and decrypt sensitive data that should be restricted to specific attribute sets or user roles.
The technical root cause of this vulnerability lies in the flawed attribute-based access control implementation within the Charm library's cryptographic primitives. When users encrypt data using DAC-MACS or MA-ABE-YJ14 schemes, the system should enforce strict attribute-based access controls that determine which users can decrypt specific ciphertexts. However, the implementation contains a logic flaw that permits unauthorized decryption by any user who can access the encryption infrastructure, effectively nullifying the cryptographic protection mechanisms. This issue manifests as a failure in the attribute verification process during decryption operations, where the system does not properly validate whether the requesting user possesses the necessary attributes to access the encrypted data.
The operational impact of this vulnerability is severe and far-reaching across organizations utilizing the Charm library for attribute-based encryption. Any malicious actor with access to a single user account or the ability to authenticate to the system can potentially decrypt data that was intended to be accessible only to specific user groups or attribute combinations. This compromises the fundamental principle of attribute-based access control and creates a pathway for unauthorized data access that could expose sensitive information including personal data, intellectual property, or confidential business information. The vulnerability affects both the DAC-MACS and MA-ABE-YJ14 schemes, indicating a systemic flaw in the library's approach to attribute-based encryption implementations.
Organizations implementing attribute-based encryption using Charm version 0.43 should immediately assess their exposure to this vulnerability and implement mitigation strategies. The primary recommendation involves upgrading to a patched version of the Charm library that addresses the attribute validation flaw in the DAC-MACS and MA-ABE-YJ14 implementations. Additionally, system administrators should conduct comprehensive audits of all data encrypted using these schemes to identify and remediate any potential unauthorized access that may have occurred. The vulnerability aligns with CWE-284 Access Control Flaws, specifically representing improper access control within cryptographic implementations. From an attack perspective, this vulnerability maps to ATT&CK technique T1552.001 Unsecured Credentials and T1078 Valid Accounts, as it allows attackers to leverage legitimate user credentials to access restricted data without proper authorization. Security teams should also consider implementing additional monitoring and logging mechanisms to detect unauthorized decryption attempts and establish more robust access control policies for cryptographic operations.
This vulnerability demonstrates the critical importance of proper cryptographic implementation and the potential consequences of access control flaws in security-critical systems. The flaw in Charm 0.43 highlights the need for comprehensive testing of cryptographic libraries, particularly in attribute-based encryption schemes where access control mechanisms are paramount to security effectiveness. Organizations relying on such cryptographic frameworks must maintain vigilance in monitoring for vulnerabilities and ensure timely patch management to prevent exploitation of similar implementation flaws that could compromise data confidentiality and integrity across their security infrastructure.