CVE-2018-5382 in BKS-V1
Summary
by MITRE
Bouncy Castle BKS version 1 keystore (BKS-V1) files use an HMAC that is only 16 bits long, which can allow an attacker to compromise the integrity of a BKS-V1 keystore. All BKS-V1 keystores are vulnerable. Bouncy Castle release 1.47 introduces BKS version 2, which uses a 160-bit MAC.
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Analysis
by VulDB Data Team • 05/12/2025
The vulnerability identified as CVE-2018-5382 affects Bouncy Castle's BKS-V1 keystore implementation, representing a significant cryptographic weakness that undermines the integrity protection mechanisms of Java keystores. This flaw specifically targets the HMAC (Hash-based Message Authentication Code) implementation used in BKS-V1 format keystores, where the authentication tag is reduced to only 16 bits in length. The limited bit length creates a substantial attack surface that allows adversaries to perform successful integrity compromise attempts against affected keystores. The vulnerability impacts all BKS-V1 keystore files regardless of their creation date or usage context, making it a pervasive issue across systems relying on this legacy keystore format. This weakness particularly affects applications and services that depend on Bouncy Castle's cryptographic libraries for secure key management and certificate handling operations.
The technical root cause of this vulnerability stems from the insufficiently strong HMAC implementation in BKS-V1 keystore files, which employs only a 16-bit HMAC value for integrity verification. This 16-bit authentication code provides minimal resistance against collision attacks and allows attackers to forge valid HMAC values with relatively low computational effort. The weakness lies in the cryptographic design choice to use a truncated HMAC rather than implementing a full-strength MAC algorithm. According to CWE-328, this represents a weakness in the cryptographic algorithm where the use of a weak hash function or truncated MAC creates insufficient security. The vulnerability enables an attacker to modify the contents of a BKS-V1 keystore file while maintaining a valid HMAC, thereby compromising the integrity of the stored certificates and private keys. This type of attack falls under the ATT&CK technique T1552.004 for "Credentials In Files" and T1499.004 for "Endpoint Denial of Service" when considering the broader impact on system security.
The operational impact of this vulnerability extends beyond simple integrity compromise, as it can lead to severe security consequences for systems relying on BKS-V1 keystores. Attackers who successfully exploit this weakness can potentially inject malicious certificates or modify existing entries within the keystore, undermining the trust model of certificate-based authentication systems. This compromise can result in man-in-the-middle attacks, certificate forgery, or unauthorized access to protected resources that depend on the keystore's integrity. The vulnerability affects a wide range of applications including web servers, application servers, and security tools that utilize Bouncy Castle's Java cryptographic libraries for SSL/TLS certificate management and secure communication protocols. Organizations using legacy systems that have not migrated from BKS-V1 to the more secure BKS-V2 format face significant risk exposure, as the 16-bit HMAC provides insufficient protection against even moderately resourced adversaries.
The recommended mitigation strategy involves immediate migration to Bouncy Castle BKS version 2 implementation, which employs a 160-bit MAC for enhanced integrity protection. This upgrade addresses the fundamental cryptographic weakness by implementing a substantially stronger authentication mechanism that provides adequate resistance against collision attacks and forgery attempts. System administrators should conduct comprehensive inventory assessments to identify all systems utilizing BKS-V1 keystores and prioritize their migration to the newer BKS-V2 format. Organizations should also implement monitoring procedures to detect potential exploitation attempts and establish secure key management practices that include regular keystore integrity verification. The transition to BKS-V2 should be accompanied by proper testing of applications to ensure compatibility with the new keystore format and that all cryptographic operations continue to function correctly. Additionally, security teams should consider implementing additional layers of protection such as file integrity monitoring and access controls to limit exposure while transitioning to the more secure implementation. This vulnerability demonstrates the critical importance of cryptographic algorithm selection and the necessity of maintaining up-to-date security practices to prevent exploitation of known weaknesses in legacy implementations.